Archive

Posts Tagged ‘malaria’

Nanotechnology against malaria parasites

December 13, 2014 Leave a comment

After maturation, malaria parasites (yellow) are leaving an infected red blood cell and are efficiently blocked by nanomimics (blue). (Fig: Modified with permission from ACS)

Malaria parasites invade human red blood cells, they then disrupt them and infect others. Researchers at the University of Basel and the Swiss Tropical and Public Health Institute have now developed so-called nanomimics of host cell membranes that trick the parasites. This could lead to novel treatment and vaccination strategies in the fight against malaria and other infectious diseases. Their research results have been published in the scientific journal ACS Nano.

For many infectious diseases no vaccine currently exists. In addition, resistance against currently used drugs is spreading rapidly. To fight these diseases, innovative strategies using new mechanisms of action are needed. The  Plasmodium falciparum that is transmitted by the Anopheles mosquito is such an example. Malaria is still responsible for more than 600,000 deaths annually, especially affecting children in Africa (WHO, 2012).

Artificial bubbles with receptors

Malaria parasites normally invade human red  in which they hide and reproduce. They then make the host cell burst and infect new cells. Using nanomimics, this cycle can now be effectively disrupted: The egressing parasites now bind to the nanomimics instead of the red blood cells.

Researchers of groups led by Prof. Wolfgang Meier, Prof. Cornelia Palivan (both at the University of Basel) and Prof. Hans-Peter Beck (Swiss TPH) have successfully designed and tested host cell nanomimics. For this, they developed a simple procedure to produce polymer vesicles – small artificial bubbles – with host cell receptors on the surface. The preparation of such polymer vesicles with water-soluble host receptors was done by using a mixture of two different block copolymers. In aqueous solution, the nanomimics spontaneously form by self-assembly.

Blocking parasites efficiently

Usually, the malaria parasites destroy their host cells after 48 hours and then infect new . At this stage, they have to bind specific host cell receptors. Nanomimics are now able to bind the egressing parasites, thus blocking the invasion of new cells. The parasites are no longer able to invade host cells, however, they are fully accessible to the immune system.

The researchers examined the interaction of nanomimics with malaria parasites in detail by using fluorescence and electron microscopy. A large number of nanomimics were able to bind to the parasites and the reduction of infection through the nanomimics was 100-fold higher when compared to a soluble form of the host cell receptors. In other words: In order to block all , a 100 times higher concentration of soluble host  is needed, than when the receptors are presented on the surface of nanomimics.

“Our results could lead to new alternative treatment and vaccines strategies in the future”, says Adrian Najer first-author of the study. Since many other pathogens use the same  receptor for invasion, the nanomimics might also be used against other . The research project was funded by the Swiss National Science Foundation and the NCCR “Molecular Systems Engineering”.

More information: Adrian Najer, Dalin Wu, Andrej Bieri, Françoise Brand, Cornelia G. Palivan, Hans-Peter Beck, and Wolfgang Meier. “Nanomimics of Host Cell Membranes Block Invasion and Expose Invasive Malaria Parasites.” ACS Nano, Publication Date (Web): November 29, 2014 | DOI: 10.1021/nn5054206

GM Mosquitos Could Eradicate Wild Populations By Only Producing Male Offspring


photo credit: James D. Gathany/CDC

Over 200 million people are infected by malaria each year, and the majority of the 627,000 deaths per year are children younger than five. The disease is carried by mosquitos who act as vectors for the parasite. It’s only transmitted to humans by female mosquitoes, as they’re the only ones who bite. A team of researchers led by Andrea Crisanti of the Imperial College London managed to genetically modify mosquitos to produce 95% male offspring, eliminating mosquito populations along with the risk of malaria. The results of the study were published in Nature Communications.

In most species of mosquito, the females need a blood meal in order to acquire the nutrients to create viable eggs. When she does, she can lay about 200 eggs at a time in water, and up to 3,000 eggs over the course of her lifetime. About half of those offspring will be daughters, many of whom will live long enough to produce that amount of offspring also. For humans living near mosquitos carrying the parasite that causes malaria, those numbers of female mosquitos present a very real threat.

But what if the numbers could be skewed so that the sex ratio favors males, who are harmless to humans? This is exactly what Crisanti’s team set out to do with Anopheles gambiae, a species of mosquito endemic to sub-Saharan Africa, where 95% of malaria deaths occur. The researchers modified the males with the enzyme I-Ppol, which excises the X chromosome during spermatogenesis. This renders sperm that would produce daughters to be non-functional, while the sperm that will create male offspring are unaffected. As a result, about 95% of the resulting offspring are male.

Next, modified males were introduced to five caged wild-type populations. As the males mated with the females, they passed along the same mutation until it dominated the population. For four of the five populations, it took only six generations for the mosquitos to die out due to a lack of females.

“What is most promising about our results is that they are self-sustaining,” co-author Nikolai Windbichler said in a press release. “Once modified mosquitoes are introduced, males will start to produce mainly sons, and their sons will do the same, so essentially the mosquitoes carry out the work for us.”

This study was the first to successfully manipulate mosquito sex ratios, and it was done in a big way. The researchers hope that this information will be used to develop genetic mutations to be used in the wild, bringing large populations of mosquitos to their knees.

“The research is still in its early days, but I am really hopeful that this new approach could ultimately lead to a cheap and effective way to eliminate malaria from entire regions,” added lead author Roberto Galizi. “Our goal is to enable people to live freely without the threat of this deadly disease.”

Of course, while eradicating the mosquitos would be fantastic for eliminating the threat of malaria, what other affects would it have? Wouldn’t there be harsh consequences for the ecosystem? After all, mosquitos have been on the planet for about 100 million years and represent 3,500 species. As it turns out, mosquitos wouldn’t really be missed if they were to disappear. While mosquitos can act as pollinators as well as a food source for other animals, their absence would be merely a temporary setback before another species filled the niche. Of course, there is a gamble in assuming the replacement organism would be harmless.

“Malaria is debilitating and often fatal and we need to find new ways of tackling it. We think our innovative approach is a huge step forward. For the very first time, we have been able to inhibit the production of female offspring in the laboratory and this provides a new means to eliminate the disease,” Crisanti explained.

Each year, sub-Saharan Africa loses about $12 billion in economic productivity due to malarial infections. Considering developed areas in these countries have per capita incomes of about US$1500, this would have very real implications for the quality of life for people in those areas. Eliminating that disease would also allow doctors and hospitals to address other health concerns, and the environment would likely benefit from not having to use insecticides.

 

REFERENCE:

Galizi, R. et al. 2014. ‘A synthetic sex ratio distortion system for the control of the human malaria mosquito’. Nature Communications, 10 June 2014.

Malaria drug treatment breakthrough

April 6, 2013 1 comment

An international study, involving researchers from Griffith University’s Eskitis Institute, has discovered a molecule which could form the basis of powerful new anti-malaria drugs.

Professor Vicky Avery from Griffith University’s Eskitis Institute is co-author of the paper “Quinolone-3-Diarylethers: a new class of drugs for a new era of malaria eradication” which has been published in the journal Science Translational Medicine.

“The 4(1H)-quinolone-3- diarylethers are selective potent inhibitors of the parasite mitochondrial cytochrome bc1 complex,” Professor Avery said.

“These compounds are highly active against the types of malaria parasites which infect humans, Plasmodium falciparum and Plasmodium vivax,” she said.

“What is really exciting about this study is that a new class of drugs based on the 4(1H)- quinolone-3- diarylethers would target the malaria parasite at different stages of its lifecycle.”

This provides the potential to not only kill the parasite in people who are infected, thus treating the clinical symptoms of the disease, but also to reduce transmission rates.

“Just one of these properties would be of great benefit but to achieve both would really make a difference in reducing the disease burden on developing nations,” Professor Avery said.

“There is also the real possibility that we could begin to impact on the incidence and spread of malaria, bringing us closer to the ultimate goal of wiping out malaria altogether.”

The selected preclinical candidate compound, ELQ-300, has been demonstrated to be very effective at blocking transmission in the mouse models.

There is a further benefit in that the predicted dosage in patients would be very low and it’s expected that ELQ-300, which has a long half-life, would provide significant protection.

The development of a new chemical class of anti-malarial drugs is very timely as the parasite is becoming increasing resistant to currently available treatments.

Eskitis Director Professor Ronald J Quinn AM said “I congratulate Professor Avery on her contribution to the discovery of this new class of anti-malarials. This is an exciting discovery that closely aligns with the Institute’s focus on global health and fighting diseases that burden the developing world. We are continuing to take the fight to malaria along a number of fronts, including targeting its many life cycle stages.”

Journal reference: Science Translational Medicine

A. Nilsen, A. N. LaCrue, K. L. White, I. P. Forquer, R. M. Cross, J. Marfurt, M. W. Mather, M. J. Delves, D. M. Shackleford, F. E. Saenz, J. M. Morrisey, J. Steuten, T. Mutka, Y. Li, G. Wirjanata, E. Ryan, S. Duffy, J. X. Kelly, B. F. Sebayang, A.-M. Zeeman, R. Noviyanti, R. E. Sinden, C. H. Kocken, R. N. Price, V. M. Avery, I. Angulo-Barturen, M. B. Jiménez-Díaz, S. Ferrer, E. Herreros, L. M. Sanz, F.-J. Gamo, I. Bathurst, J. N. Burrows, P. Siegl, R. K. Guy, R. W. Winter, A. B. Vaidya, S. A. Charman, D. E. Kyle, R. Manetsch, M. K. Riscoe, Quinolone-3-Diarylethers: A New Class of Antimalarial Drug. Sci. Transl. Med. 5, 177ra37 (2013).

Provided by: Griffith University

Biologists Produce Potential Malarial Vaccine from Algae

May 25, 2012 1 comment

Biologists at the University of California, San Diego have succeeded in engineering algae to produce potential candidates for a vaccine that would prevent transmission of the parasite that causes malaria, an achievement that could pave the way for the development of an inexpensive way to protect billions of people from one of the world’s most prevalent and debilitating diseases. Initial proof-of-principle experiments suggest that such a vaccine could prevent malaria transmission.

(up) The edible algae Chlamydomonas, seen here at UC San Diego, can be grown in ponds anywhere in the world. (Credit: SD-CAB)

Malaria is a mosquito-borne disease caused by infection with protozoan parasites from the genus Plasmodium. It affects more than 225 million people worldwide in tropical and subtropical regions, resulting in fever, headaches and in severe cases coma and death. While a variety of often costly antimalarial medications are available to travelers in those regions to protect against infections, a vaccine offering a high level of protection from the disease does not yet exist.

The use of algae to produce malaria proteins that elicited antibodies against Plasmodium falciparum in laboratory mice and prevented malaria transmission was published May 16 in the online, open-access journal PLoS ONE. The development resulted from an unusual interdisciplinary collaboration between two groups of biologists at UC San Diego — one from the Division of Biological Sciences and San Diego Center for Algae Biotechnology, which had been engineering algae to produce bio-products and biofuels, and another from the Center for Tropical Medicine and Emerging Infectious Diseases in the School of Medicine that is working to develop ways to diagnose, prevent and treat malaria.

Part of the difficulty in creating a vaccine against malaria is that it requires a system that can produce complex, three-dimensional proteins that resemble those made by the parasite, thus eliciting antibodies that disrupt malaria transmission. Most vaccines created by engineered bacteria are relatively simple proteins that stimulate the body’s immune system to produce antibodies against bacterial invaders. More complex proteins can be produced, but this requires an expensive process using mammalian cell cultures, and the proteins those cells produce are coated with sugars due to a chemical process called glycosylation.

“Malaria is caused by a parasite that makes complex proteins, but for whatever reason this parasite doesn’t put sugars on those proteins,” said Stephen Mayfield, a professor of biology at UC San Diego who headed the research effort. “If you have a protein covered with sugars and you inject it into somebody as a vaccine, the tendency is to make antibodies against the sugars, not the amino acid backbone of the protein from the invading organism you want to inhibit. Researchers have made vaccines without these sugars in bacteria and then tried to refold them into the correct three-dimensional configuration, but that’s an expensive proposition and it doesn’t work very well.”

Instead, the biologists looked to produce their proteins with the help of an edible green alga, Chlamydomonas reinhardtii, used widely in research laboratories as a genetic model organism, much like the fruit fly Drosophila and the bacterium E. coli. Two years ago, a UC San Diego team of biologists headed by Mayfield, who is also the director of the San Diego Center for Algae Biotechnology, a research consortium seeking to develop transportation fuels from algae, published a landmark study demonstrating that many complex human therapeutic proteins, such as monoclonal antibodies and growth hormones, could be produced by Chlamydomonas.

That got James Gregory, a postdoctoral researcher in Mayfield’s laboratory, wondering if a complex protein to protect against the malarial parasite could also be produced by Chlamydomonas. Two billion people live in regions where malaria is present, making the delivery of a malarial vaccine a costly and logistically difficult proposition, especially when that vaccine is expensive to produce. So the UC San Diego biologists set out to determine if this alga, an organism that can produce complex proteins very cheaply, could produce malaria proteins that would inhibit infections from malaria.

“It’s too costly to vaccinate two billion people using current technologies,” explained Mayfield. “Realistically, the only way a malaria vaccine will ever be used is if it can be produced at a fraction of the cost of current vaccines. Algae have this potential because you can grow algae any place on the planet in ponds or even in bathtubs.”

Collaborating with Joseph Vinetz, a professor of medicine at UC San Diego and a leading expert in tropical diseases who has been working on developing vaccines against malaria, the researchers showed that the proteins produced by the algae, when injected into laboratory mice, made antibodies that blocked malaria transmission from mosquitoes.

“It’s hard to say if these proteins are perfect, but the antibodies to our algae-produced protein recognize the native proteins in malaria and, inside the mosquito, block the development of the malaria parasite so that the mosquito can’t transmit the disease,” said Gregory.

“This paper tells us two things: The proteins that we made here are viable vaccine candidates and that we at least have the opportunity to produce enough of this vaccine that we can think about inoculating two billion people,” said Mayfield. “In no other system could you even begin to think about that.”

The scientists, who filed a patent application on their discovery, said the next steps are to see if these algae proteins work to protect humans from malaria and then to determine if they can modify the proteins to elicit the same antibody response when the algae are eaten rather than injected.

Other UC San Diego scientists involved in the discovery were Fengwu Li from Vinetz’s laboratory and biologists Lauren Tomosada, Chesa Cox and Aaron Topol from Mayfield’s group. The basic technology that led to the development was supported by the Skaggs family. The research was supported by grants from the National Institute of Allergy and Infectious Diseases and the San Diego Foundation. The California Energy Commission supported work on recombinant protein production for biofuels use, and this technology helped enabled these studies.

Story Source:

The above story is reprinted from materials provided by University of California – San Diego.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Gregory JA, Li F, Tomosada LM, Cox CJ, Topol AB, et al.Algae-Produced Pfs25 Elicits Antibodies That Inhibit Malaria TransmissionPLoS ONE, 2012 DOI:10.1371/journal.pone.0037179

New Treatment for Malaria Tertiana


“Malaria tertiana is the form of malaria that science needs to focus on in more detail in future.” These are the words of Harald Noedl from the Institute of Specific Prophylaxis and Tropical Medicine at the Medical University of Vienna, spoken as part of World Malaria Day on Wednesday, 25th April. In a multi-centre study, the MedUni Vienna team, led by Harald Noedl, is working on an improved and more straightforward treatment of this form of malaria.

Although malaria tropica, which currently kills around 655,000 people a year (around 2,000 people every day), has increasingly been repressed as a result of more research, malaria tertiana may well develop into the main problem of the future in many countries, says Noedl. The problem does not so much involve the (low) mortality rate from malaria tertiana, but rather the often protracted period of illness that can occur as a result of the condition. This is because if the malaria tertiana pathogens are not killed with targeted therapy, they can remain dormant in the human liver for months or even years, and cause recurrent relapses.

Conventional therapy involves administering chloroquine for three days, followed by two weeks of primaquine therapy. “However unlike in Europe, compliance with medications in tropical countries is often very poor,” explains the malaria expert from the MedUni Vienna. Many patients would discontinue the medication after just a few days.

As a consequence, the pathogens will survive in the liver and can cause an outbreak of malaria tertiana at any time which is as infectious as the other two forms of malaria. This makes patients a constant source of infection for their environment and the new condition is often no longer associated with the previous episode of malaria and therefore treated incorrectly. Says Noedl: “This makes patients, most of whom are the poorest of the poor, constantly ill, preventing them from working. It’s a fatal vicious circle.”

In a multi-centre study involving the MedUni Vienna, scientists are well on their way to establishing a new substance (tafenoquine). The advantage of this is that the drug only has to be taken for a maximum of three days. Tafenoquine is currently undergoing clinical trials.

MedUni Vienna and new malaria focus in Africa

Since 2006, the Center for Geographic Medicine at the MedUni Vienna’s MARIB research center, led by Harald Noedl, has been working on malaria research in Bangladesh. More than 20,000 patients have been treated free of charge since. In 2012, the MedUni expanded its malaria focus to include Africa, and in particular Ethiopia. There, the MedUni team is cooperating with the University of Gondar in the north west of the country. Says Noedl: “We are keen to further the MedUni Vienna’s position as a leading centre for malaria expertise, lead multi-center studies and establish a global malaria network.”

Source:

The above story is reprinted (with editorial adaptations by MedicalXpress staff) from materials provided by Medical University of Vienna (news : web)

Notre Dame researchers report fundamental malaria discovery

February 11, 2012 1 comment

A team of researchers led by Kasturi Haldar and Souvik Bhattacharjee of the University of Notre Dame’s Center for Rare and Neglected Diseases has made a fundamental discovery in understanding how malaria parasites cause deadly disease.

The researchers show how parasites target proteins to the surface of the red blood cell that enables sticking to and blocking blood vessels. Strategies that prevent this host-targeting process will block disease.

The research findings appear in the Jan. 20 edition of the journal Cell, the leading journal in the life sciences. The study was supported by the National Institutes of Health.

Malaria is a blood disease that kills nearly 1-3 million people each year. It is caused by a parasite that infects red cells in the blood. Once inside the cell, the parasite exports proteins beyond its own plasma membrane border into the blood cell. These proteins function as adhesins that help the infected red blood cells stick to the walls of blood vessels in the brain and cause cerebral malaria, a deadly form of the disease that kills over half a million children each year.

In all cells, proteins are made in a specialized cell compartment called the endoplasmic reticulum (ER) from where they are delivered to other parts of the cell. Haldar and Bhattacharjee and collaborators Robert Stahelin at the Indiana University School of Medicine – South Bend (who also is an adjunct faculty member in Notre Dame’s Department of Chemistry and Biochemistry), and David and Kaye Speicher at the University of Pennsylvania’s Wistar Institute discovered that for host-targeted malaria proteins the very first step is binding to the lipid phosphatidylinositol 3-phosphate, PI(3)P, in the ER.

This was surprising for two reasons. Previous studies suggested an enzyme called Plasmepsin V that released the proteins into the ER was also the export mechanism. However, Haldar, Bhattacharjee and colleagues discovered that binding to PI(3)P lipid which occurs first is the gate keeper to control export and that export can occur without Plasmepsin V action. Further, in higher eukaryotic cells (such as in humans), the lipid PI(3)P is not usually found within the ER membrane but rather is exposed to the cellular cytoplasm.

Haldar and Bhattacharjee are experts in malaria parasite biology and pathogenesis. Stahelin is an expert in PI(3)P lipid biology, and David and Kaye Speicher are experts in proteomics and a method called mass spectrometry.

Story Source:

The above story is reprinted (with editorial adaptations by MedicalXpress staff) from materials provided by University of Notre Dame (news : web)

Scientists Characterize Protein Essential to Survival of Malaria Parasite

January 11, 2012 Leave a comment

A biology lab at Washington University has just cracked the structure and function of a protein that plays a key role in the life of a parasite that killed 655,000 people in 2010.

A cartoon based on the electron density map makes it easier to see the protein’s structure and figure out how it works. The enzyme’s job is to add a methyl group — three times — to a starting molecule as part of a process for making cell membranes. In this cartoon, the phosphate is a stand-in for the starting molecule and the green molecule is the one that donates a methyl group. Both are positioned in the active site of the enzyme, the pocket where the chemistry takes place. (Credit: Jez)

The protein is an enzyme that Plasmodium falciparum, the protozoan that causes the most lethal form of malaria, uses to make cell membrane.

The protozoan cannot survive without this enzyme, but even though the enzyme has many lookalikes in other organisms, people do not make it. Together these characteristics make the enzyme an ideal target for new antimalarial drugs.

The research was published in the January 6 issue of the Journal of Biological Chemistry (JBC) as “Paper of the Week” for that issue.

The work also will be featured in ASBMB Today (the newsletter of the American Society for Biological Molecular Biology, which publishes JBC).

Sweating the cold room

The protein’s structure might have remained an enigma, had it not been the “unreasonable optimism” of Joseph Jez, PhD, associate professor of biology in Arts & Sciences, which carried his team through a six-year-long obstacle course of failures and setbacks.

“What my lab does is crystallize proteins so that we can see what they look like in three dimensions,” Jez says. “The idea is that if we know a protein’s structure, it will be easier to design chemicals that would target the protein’s active site and shut it down,” Jez says.

The latest discovery is the culmination of a project that began years before when Jez was working at the Danforth Plant Science Center in St. Louis and collaborating with scientists at the local biotech startup Divergence. “At the time, C. elegans had just been sequenced and the Divergence scientists were looking at using it as an easy model to work out the biochemistry of parasitic nematodes,” Jez says.

C. elegans is a free-living nematode, or microscopic roundworm, but many nematodes are parasitic and cause disease in plants, livestock and people.

During this project, Lavanya Palavalli, a summer intern working with Jez, crystallized the C. elegans version of the enzyme. The job of the enzyme, phosphoethanolamine methyltransferase, thankfully abbreviated to PMT, is to add methyl groups to a starting molecule, phosophoethanolamine.

“When Soon Goo Lee later took up the project,” says Jez, “the plan was to try to grow better crystals of the C. elegans protein, ones good enough to get readable X-ray diffraction patterns.

Two years later, the crystals were looking better but still not good enough.

So Jez suggested that Lee go after homologous (look-alike) proteins in other organisms. “Even though the proteins are homologous, each has a different amino acid sequence and so will behave differently in the crystallizations,” Jez says. “Lee went from working with two C. elegans proteins to three plant proteins, two other nematode proteins and then the Plasmodium protein,” Jez says.

“He took all six of those PMT versions into the crystallization trials to maximize his odds,” Jez says.

“To crystallize a protein,” Jez says, “we put a solution of a salt or something else that might work as a desiccant in the bottom of a small well. And then we put a drop of our liquid protein on a microscope cover slip and flip it over the top of the well, so the drop of protein is hanging upside down in the well.”

“What we’re trying to do is to slowly withdraw water from the protein. It’s exactly like making rock candy, only in that case, the string hanging into the jar of sugar solution helps to withdraw water,” he says.

The difference is that sugar wants to form crystals and proteins are reluctant to do so.

“There are 24 wells to a tray, and we usually screen 500 wells per protein at first,” Jez says. “Lee had eight proteins and so his first pass was to screen 4,000 conditions. And then he had to try different combinations of ligands to the proteins and crystallize those. This is why it took a few years to finally get where he needed to go.”

Road trip!

 The scientists need crystals — preferably nice, big ones — to stick in the path of an X-ray beam at Argonne National Laboratory in Chicago. (If the crystal is a good one, and all the atoms are lined up in a repeating array, the scattered X-rays will produce a clear pattern of spots.)

Embedded in that pattern is the mathematical information needed to back-calculate to the position of the atoms in the protein, a process a bit like throwing a handful of pebbles in a lake and then calculating where they landed by the pattern of waves arriving at the shoreline.

Lee got the PMT from Haemonchus contortus to crystallize first, but there were technical issues with the diffraction pattern that would have made solving it technically and computationally very demanding.

“When the Plasmodium enzyme finally crystallized, Soon got four crystals kind of stacked on top of each other and each of them was paper thin,” Jez says.

“I never thought it would work, but we took them to Argonne anyway and he actually did surgery under the microscope and cracked off a little tiny piece of it.”

To everyone’s surprise, he got a clean diffraction pattern from the crystal. “Because the Plasmodium enzyme was the smallest one and the easiest to work on, we pushed that one first,” Jez says.

The moment of truth

“Once we had a Plasmodium crystal that was diffracting really well, we could try back-calculating to see whether we could extract the atom positions from the data,” Jez says.

After the computer finished its calculations, Lee clicked a mouse button to see the results, which would reveal whether his years of work finally would pay off.

When Lee clicked the mouse, he got an electron density map in exceptionally sharp focus.

“When you see a map like that, it’s like suddenly the wind has kicked up and you’re sailing free,” Jez says, “because there’s this moment, like, before you click that button, no one has ever seen how this protein is put together in three dimensions. You’re the first person to ever see it.

“The irony of it is we got such good quality diffraction pattern and electron density maps off such an ugly crystal,” he says.

Lock and load

“Once you have the electron density map, the task is to build a structure that matches the amino acid sequence of the protein,” Jez says.

“The first thing you do is put in the amino acid backbones and connect them together to form a chain. It’s like having a long thread, each inch of which is an amino acid, and your job is to take that thread and move it in three dimensions through that electron density map.”

The next step is to add the side chains that make one amino acid different from another, Jez says. “The amino acid sequence is known,” he says. “Your goal is to match the way you string together the amino acids in the electron density map to that sequence.”

“Once you have the overall structure, you can start to figure out how the enzyme works. The PMT enzyme is trying to join two molecules,” Jez says. “To do that, it has to lock them in place so that the chemistry can happen, and then it has to let go of them.

“We think the protein has a lid that opens and closes,” he says. “The active site stays open until the substrates enter, and then the lid clamps down, and when it clamps down it actually puts the substrates together.”

Calling Bill and Melinda Gates

Not only do infections by Plasmodium falciparum cause the most severe form of malaria, about 40 percent of the human population lives in areas where the parasite is endemic. Moreover, drugs that used to be effective against malaria are beginning to fail, in part because widespread drug counterfeiting has led to resistance.

New anti-malarial drugs are desperately needed, and the PMT protein is an ideal target. If PMT is disabled, the protozoan can’t make cell membranes and it dies. Moreover, a drug that would kill Plasmodium might have minimal side effects on patients.

Although the process of identifying compounds that would target PMT is in the early stages, a handful of anti-parasitical compounds used to treat diseases are known to block PMT as well.

As for Lee, he has had a hard go of it, but now things are breaking his way. Plasmodium PMT is giving up its secrets, and the plant and nematode PMTs are coming along as well.

When he clicked the mouse button and a clean electron density map came up, he says, it was like seeing “the light at the end of a five-year-long tunnel.”

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Washington University in St. Louis.

Journal Reference:

S. G. Lee, Y. Kim, T. D. Alpert, A. Nagata, J. M. Jez.Structure and Reaction Mechanism of Phosphoethanolamine Methyltransferase from the Malaria Parasite Plasmodium falciparum: AN ANTIPARASITIC DRUG TARGETJournal of Biological Chemistry, 2011; 287 (2): 1426 DOI:10.1074/jbc.M111.315267