Wednesday, February 22, 2012
Despite chimps being the older species, their MHC genes are less polymorphic than humans. To quantify this reduced polymorphism, Can Kesmir's group from the Netherlands compared the protein binding repertoire of MHC genes between chimps and humans. They utilized the proteomes of over 900 mammalian viruses and showed that binding efficiency at two chimp loci (A and B) show different degrees of reduction. Specifically, class A molecules have 36% lower binding than the human analogues, whereas class B molecules only show a 15% reduction. They further found that class A molecules are much more similar to each other than class B molecules, supporting the idea that class A molecules show signs of a selective sweep in chimps. The agent causing this sweep is thought be an ancestral HIV-like virus, and their results do indeed show high binding efficiency of the HIV virus to chimp class A molecules. However, they found two other viruses in their library with binding efficiencies greater than the HIV virus. Unfortunately, their experiment was inconclusive as to whether or not these newly identified viruses could have caused the selective sweep.