Crystallization and preliminary structure determination of an intact humanimmunoglobulin, b12: an antibody that broadly neutralizes primary isolatesof HIV-1

An intact human immunoglobulin with a full-length hinge has been crystalliz ed for the first time in a form in which all of the Ig domains are ordered. The IgG1 antibody b12 is one of only three known monoclonal antibodies des cribed that potently neutralize a broad range of HIV-1 primary isolates. It binds to an epitope overlapping the conserved CD4 binding site on the vira l surface antigen gp120. Hexagonal crystals corresponding to space group R3 2 were grown from 0.8 M ammonium sulfate, with unit-cell parameters a = b = 271.3, c = 175.2 Angstrom and one molecule per asymmetric unit. The crysta ls diffract to 2.8 Angstrom and a preliminary molecular-replacement solutio n indicates that all 12 Ig domains of the antibody can be resolved.