A genetic analysis of the HIV-1env binding site on the human CD4 receptor
The CD4 molecule is a human T cell surface glycoprotein that interacts with the envelope glycoprotein of the human immunodeficiency virus, HIV-1, thus serving as a cellular receptor for this virus. To define the sites on CD4 essential for binding to gp120, several truncated, soluble derivatives of CD4 were constructed and produced. In addition, a series of 26 CD4 substitution mutants were also constructed. Quantitative binding analysis of the truncated proteins demonstrates that the determinants for high affinity HIV-1 envelope binding reside solely within the first 106 amino acids of CD4 (the V1 domain), a region having significant sequence homology to immunoglobulin variable regions. Analysis of the substitution mutants further defines a discreet binding site within this domain that overlaps a region structurally homologous to the second complementarity determining region of antibody variable domains. This analysis was extended further by mapping the epitopes of 25 CD4 monoclonal antibodies (mAbs). The majority of the mAb epitopes reside in the first two amino terminal V domains of CD4. Importantly, each of the mAb epitopes maps to regions which an immunoglobulin light chain model would predict to comprise exposed surfaces or loops. A number of mAbs reacted with sites distant on a linear map, but which, based on an immunoglobulin V domain model should lie close in space. These results demonstrate that CD4 shares structural characteristics with immunoglobulin light chain domains. To further examine the structural determinants necessary for HIV-1 envelope binding to CD4, small deletions were created at the amino and carboxy terminus of a soluble V1 protein. Quantitative analysis of these deletion mutants showed that even small deletions within the putative "framework" structure of V1 has highly disruptive effects on the conformation of the domain, in particular gp120 bindings.
Arthos, James, "A genetic analysis of the HIV-1env binding site on the human CD4 receptor" (1990). Dissertations available from ProQuest. AAI9026514.