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). A variant of the wild-type gp120 was generated similarly. This variant contained a mutation on the center of the CD4 binding site known as the """"""""Phe 43 cavity"""""""". This mutation stabilized the CD4-state of gp120 and increased CD4 affinity 10-to-20-fold. 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 indicated that the CD4-state trimers elicited an enhanced neutralizing profile compared to wild-type glycoprotein trimers are interesting platforms for further modification to better elicit broadly neutralizing antibodies (published). 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). We are also testing SF162 gp120 trimers with selected trimerization motifs to be recongized by the SF162 trimer-specific, strain-neutralizing antibody 2909 from NYU for potential co-crystal studies. Adhuna Phogat is leading this project. We may test the 2909 antibody in combination with other selected antibodies for enhanced neutralization of SF162 and other strains of HIV-1.