Protein Structure Key For AIDS, Cell Function

Levels of the protein climb, for reasons unknown, when people fall ill, making human CD38 a marker for these diseases.

Asone example, researchers have shown that CD38 interrupts an interactionbetween the AIDS virus and its point of entry into cells -- a proteinreceptor called CD4. By looking at CD38's 3-D structure, the Cornellresearchers identified a peptide, an organic compound composed of aminoacids, that they believe may play a role in interrupting the interfacebetween CD4 and HIV-AIDS.

The findings, published in the journalStructure (Vol. 13, Sept. 2005), mark a major step toward designingdrugs that could inhibit processes related to certain diseases. Knowingthe protein's structure also opens the door to understanding CD38'smany functions related to key biological processes about whichresearchers know very little.

"For example, the mechanism of howa cell mediates calcium release is largely unknown," said the paper'ssenior author, Quan Hao, director of the Macromolecular DiffractionFacility (MacCHESS), the biomedical research arm of the Cornell HighEnergy Synchrotron Source (CHESS). "So this is a very fundamentalquestion for biologists."

It turns out that CD38 helps produce atleast two calcium messenger molecules, each of which then openschannels for the release of calcium from specific stores, orreservoirs, within cell organelles.

High intensity X-rays made itpossible to pass photons through a protein crystal to reveal itsstructure. Cornell's synchrotron produces beams of X-rays millions oftimes more intense than conventional X-ray generators allow. The veryintense beams were necessary to determine the atomic structure of CD38.The research group, which includes researchers from the University ofMinnesota, also developed new calculations that allowed them to extractthe protein's entire structure from the X-ray images.

Byrevealing CD38's detailed structure, scientists can now begin toexamine how the protein's form influences its molecular functions.

"People have been struggling with this for a long time, and we have finally solved it," said Hao.

TheNational Institutes of Health, which supports MacCHESS, also fundedthis research. The paper's other lead authors include MacCHESS graduatestudent Qun Liu and researcher support specialist Irina Kriksunov.