X-ray analysis at 2.0 A resolution of mouse submaxillary renin complexed with a decapeptide inhibitor CH-66, based on the 4-16 fragment of rat angiotensinogen.

The structure of mouse submaxillary renin complexed with a decapeptide inhibitor, CH-66 (Piv-His-Pro-Phe-His-Leu-OH-Leu-Tyr-Tyr-Ser-NH2), where Piv denotes a pivaloyl blocking group, and -OH- denotes a hydroxyethylene (-(S)CHOH-CH2-) transition state isostere as a scissile bond surrogate, has been refined to an agreement factor of 0.18 at 2.0 A resolution. The positions of 10,038 protein atoms and 364 inhibitor atoms (4 independent protein inhibitor complexes), as well as of 613 solvent atoms, have been determined with an estimated root-mean-square (r.m.s.) error of 0.21 A. The r.m.s. deviation from ideality for bond distances is 0.026 A, and for angle distances is 0.0543 A. We have compared the three-dimensional structure of mouse renin with other aspartic proteinases, using rigid-body analysis with respect to shifts involving the domain comprising residues 190 to 302. In terms of the relative orientation of domains, mouse submaxillary renin is closest to human renin with only a 1.7 degrees difference in domain orientation. Porcine pepsin (the molecular replacement model) differs structurally from mouse renin by a 6.9 degrees domain rotation, whereas endothiapepsin, a fungal aspartic proteinase, differs by 18.8 degrees. The triple proline loop (residues 292 to 294), which is structurally opposite the active-site "flap" (residues 72 to 83), gives renin a superficial resemblance to the fold of the retroviral proteinases. The inhibitor is bound in an extended conformation along the active-site cleft, and the hydroxyethylene moiety forms hydrogen bonds with both catalytic aspartate carboxylates. The complex is stabilized by hydrogen bonds between the main chain of the inhibitor and the enzyme. All side-chains of the inhibitor are in van der Waals contact with groups in the enzyme and define ten specificity sub-sites. This study shows how renin has compact sub-sites due to the positioning of secondary structure elements, to complementary substitutions and to the residue composition of its loops close to the active site, leading to extreme specificity towards its prohormone substrate, angiotensinogen. We have analysed the micro-environment of each of the buried charged groups in order to predict their ionization states.