In this study, we have produced soluble versions of just the HIV-1 Env gp120 receptor binding domain derived from a primary isolate stabilized by heterologous trimerization motifs (GCN4). We have produced milligram quantities of these proteins and and performed a detailed biochemical and biophysical analysis. We have tested these glycoproteins for immunogenicity in rabbits . Breadth of neutralization indicate that these glycoproteins are interesting platforms for further modification to better elicit broadly neutralizing antibodies. A second goal of this study is to obtain crystal structures of these trimeric HIV-1 gp120 glycoproteins. Dr. Pancera will conduct structural studies on these proteins as well as full length gp120 glycoproteins that she has produced in the Wyatt laboratory as part of her doctoral studies (completed April 2005).