High-resolution solution NMR structure of the minimal active domain of the human immunodeficiency virus type-2 nucleocapsid protein.

The retroviral nucleocapsid (NC) protein is a multifunctional protein essential for RNA genome packaging and viral infectivity. The NC protein, NCp8, of the human immunodeficiency virus type-II (HIV-2) is a 49 amino acid peptide containing two zinc fingers, of the type C-X2-C-X4-H-X4-C, connected by seven amino acid residues, called the "basic amino acid cluster." It has been shown that the N-terminal zinc finger flanked by the basic amino acid cluster is the minimal active domain for the specific binding to viral RNA and other functions. However, the structure-activity relationships of NCp8 have not been investigated in detail. In the present study, the three-dimensional structure of a 29 amino acid peptide, including the minimal active domain (NCp8-fl), was determined by two-dimensional 1H NMR spectroscopy with simulated annealing calculations. A total of 15 converged structures of NCp8-fl were obtained on the basis of 355 experimental constraints, including 343 distance constraints obtained from nuclear Overhauser effect connectivities, 12 torsion angle (phi, chi1) constraints, and four constraints for zinc binding. The root-mean-square deviation of the 15 converged structures was 0.29 +/- 0.04 A for the backbone atoms (N, C(alpha), C) and 1.27 +/- 0.13 A for all heavy atoms. Interestingly, the basic amino acid cluster itself was defined well, with a loop-like conformation in which three arginine residues in the cluster and one arginine residue in the zinc finger are located approximately in the same plane of the molecule and are exposed to the solvent. The structure-activity relationships are discussed on the basis of the comparison of this well-defined structure with those of other NC proteins.