CRYSTAL-STRUCTURE OF DIMERIC HIV-1 CAPSID PROTEIN

X-ray diffraction analysis of a human immunodeficiency virus (HIV-1) c apsid (CA) protein shows that each monomer within the dimer consists o f seven alpha-helices, five of which are arranged in a coiled coil-lik e structure. Sequence assignments were made for two of the helices, an d tentative connectivity of the remainder of the protein was confirmed by the recent solution structure of a monomeric N-terminal fragment. The C-terminal third of the protein is mostly disordered in the crysta l. The longest helices in the coiled coil-like structure are separated by a long, highly antigenic peptide that includes the binding site of an antibody fragment complexed with CA in the crystal. The site of bi nding of the Fab, the position of the antigenic loop and the site of c leavage between the matrix protein and CA establish the side of the di mer that would be on the exterior of the retroviral core.