KINETIC AND MODELING STUDIES OF SUBSITES S-4-S-3' OF MOLONEY MURINE LEUKEMIA-VIRUS PROTEASE

The substrate specificity of the Moloney murine leukemia virus proteas e (Mo-MuLV PR) was analyzed by using the oligopeptide substrate Val-Se r-Gln-Asn-Tyr down arrow Pro-Ile-Val-Gln-NH2 and a series of analogs c ontaining single amino acid substitutions in the P-4-P-3' positions. M o-MuLV PR appears to act similarly to the human immunodeficiency virus (HIV) PRs, except for peptides having substitutions at P-4 and P-2 po sitions. Mo-MuLV PR shows a strong preference for the analogs having h ydrophobic residues, such as Val or Ile at P-4, and Ile and Leu at P-2 , in contrast to HIV-1 and HIV-2 PRs, which prefer smaller or more pol ar residues at both positions. We built a molecular model of Mo-MuLV P R on the basis of the crystal structure of the related HIV PR. Althoug h the overall structure of Mo-MuLV PR is predicted to be close to that of HIV-1 PR, almost all of the residues forming the subsites are diff erent. The increased hydrophobicity due to the pro(12) insertion and t he presence of more aromatic residues in the S-4 subsite of Mo-MuLV PR compared to HIV-1 and HIV-2 PRs can be correlated with the observed d ifferences using P-4-substituted analogs of VSQNYPIVQ. The preference of Mo-MuLV PR for larger hydrophobic residues at the P-2 position can be correlated with the larger size of its S-2 subsite, due in part to the presence of Val(39) Ala(57), and His(84) in Mo-MuLV PR, instead of Ile(32), Ile(50), and Met(76), respectively, as occurs in HIV-2 PR.