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January 18, 2006
California Aggie

Following the Mosquito's Nose
UCD Researchers Study How the Mosquito Gets Its Sense of Smell
By Kari Fish
Aggie Science Writer

David Wilson and graduate student Mark Wogulis used X-ray technology to map AgamOPBI, a protein pivotal to a mosquito's sense of smell. (Graphic/Mark Wogulis)

Mosquitoes need their sense of smell for many important life decisions such as selecting a tasty blood meal and finding a nice waterhole in which to lay their eggs. And, according to researchers at UC Davis, understanding just how they smell might lead to ways to prevent the spread of disease.

David Wilson, a UC Davis professor of molecular and cellular biology, recently published the advancements he and others made in understanding the chemical mechanisms behind mosquitoes' sense of smell, which may eventually lead to methods of impairing their ability to infect humans, he said.

Mosquitoes bring in scent molecules via the thousands of little hairs on their antennae, according to Walter Leal, a UC Davis entomology professor who was involved in the study. Once inside the mosquito, the scent molecules are picked up by odorant-binding proteins that act as intermediaries, delivering the scent molecules to receptor cells, he noted.

While Leal's lab primarily researches West Nile Virus in California, as a side project it discovered the odorant-binding protein present in Anopheles gambiae, the species of mosquito that is one of the primary vectors of malaria. Wilson, along with graduate student Mark Wogulis, used X-ray technology to determine the crystal structure of this protein, called AgamOPB1.

They discovered a long "sausagelike" tunnel through the center of the protein, which holds scent molecules. This shape differs in the few other odorant-binding proteins whose structures have been discovered in other insects; scent molecules are held in a smaller pocket or are picked up through folding of the protein.

Researchers also determined that AgamOPB1 changes shape when its pH level drops, when it becomes more acidic. This phenomenon is also seen in the other known odorant-binding proteins and results in the release of the protein's molecular contents. The current hypothesis, according to Wilson, is that the odorant-binding protein transfers the scent molecules to a receptor via a pH gradient.

"Now we understand how mosquitoes more or less smell a human meal," Wilson said.

Female mosquitoes feed after they mate; they need a blood meal to fertilize their eggs. Researchers are now looking for what the mosquito's target scent molecule is in finding its blood source.

"We are not sure what the human odorant is," said Wilson, "but based on the shape of the protein we can guess what it looks like."

Scent molecules are held in the protein's long tunnel structure, which researchers can study to determine what molecules would and would not fit in it.

This research is a very big project, with two sides to it, according to Leal. There is the basic research end, while the impairment of the mosquito's sense of smell is a possible application down the road, said Wilson.

Wogulis has had firsthand experience of the effects of malaria as a Peace Corps volunteer teaching science in Africa. Little did he know he would later be involved in research on the biology of the malaria vector, he said.

"We hope to figure out some way to stop mosquitoes from infecting people," said Wogulis.

KARI FISH can be reached at science@californiaaggie.com.

Note: The research is published in the Jan. 6 issue of Biochemical and Biophysical Research Communications.

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