For a number of viruses, oligomerization is a critical component of envelope processing and surface expression. Previously, we reported that a synthetic peptide (DP-107) corresponding to the putative leucine zipper region (aa 553-590) of the transmembrane protein (gp4l) of human immunodeficiency virus type 1 (HIV-1) exhibited a-helical secondary structure and self-associated as a coiled coil. In view of the tendency of this type of structure to mediate protein association, we speculated that this region of gp4l might play a role in HIV-1 envelope oligomerization. However, later it was shown that mutations which should disrupt the structural elements of this region of gp4l did not affect envelope processing, transport, or surface expression (assembly oligomerization). In this report we compare the effects of amino acid substitutions within this coiled-coil region on structure and function of both viral envelope proteins and the corresponding synthetic peptides. Our results establish a correlation between the destabilizing effects of amino acid substitutions on coiledcoil structure in the peptide model and phenotype of virus entry. These biological and physical biochemical studies do not support a role for the coiled-coil structure in mediating the assembly oligomerization of HIV-1 envelope but do imply that this region of gp4l plays a key role in the sequence of events associated with viral entry. We propose a functional role for the coiled-coil domain of HIV-1 gp4l.

Carbonic anhydrase II (CAII) is a zinc metalloenzyme that catalyzes the hydration of CO 2 to yield bicarbonate and a proton. N-(4-Sulfamylbenzoyl)benzylamine (SBB) is a tight-binding inhibitor of human CAII with K d ) 2.1 nM. Previous X-ray crystallographic work shows that the benzyl ring of SBB makes an edge-to-face interaction with Phe-131 in the enzyme active site. We have manipulated the electrostatics of this interaction by systematically substituting electronegative fluorine atoms for the benzyl ring hydrogens of SBB. Crystal structures of 10 enzyme-inhibitor complexes have been determined to atomic resolution. Analysis of these structures reveals that the main contributions to enzyme-inhibitor affinity can be approximated by a combination of dipole-induced dipole, dipole-quadrupole, and quadrupole-quadrupole interactions. Surprisingly, different electrostatic components dominate affinity in different enzyme-inhibitor pairs.