SOLUTION STRUCTURE OF CYANOVIRIN-N, A POTENT HIV-INACTIVATING PROTEIN

The solution structure of cyanovirin-N, a potent 11,000 M-r HIV-inacti vating protein that binds with high affinity and specificity to the HI V surface envelope protein gp120, has been solved by nuclear magnetic resonance spectroscopy, including extensive use of dipolar couplings w hich provide a priori long range structural information. Cyanovirin-N is an elongated, largely beta-sheet protein that displays internal two -fold pseudosymmetry. The two sequence repeats (residues 1-50 and 51-1 01) share 32% sequence identity and superimpose with a backbone atomic root-mean-square difference of 1.3 Angstrom. The two repeats, however , do not form separate domains since the overall fold is dependent on numerous contacts between them. Rather, two symmetrically related doma ins are formed by strand exchange between the two repeats. Analysis of surface hydrophobic clusters suggests the location of potential bindi ng sites for protein-protein interactions.