Structure of a ternary complex of proteinase K, mercury and a substrate analogue heptapeptide amide Ac-Pro-Ala-Pro-Phe-Ala-Ala-Ala-NH_2 at 2.3 A resolution

摘要

The structure indicates an alternate inhibitor binding site of proteinase K. The crystal structure of a ternary complex of proteinase K, Hg(II) and heptapeptide amide Ac-Pro-Ala-Pro-Phe-Ala-Ala-Ala-NH_2 has been determined at 2.3 A resolution and refined to an R-factor of 0.169 for 11538 reflections. The mercury atom occupies two alternate sites with occupancies of 0.80 and 0.20 respectively. The Hg(II) at both sites interacts with Cys-73 S~γ. The mercury at both sites forms regular polyhedra involving atoms from residues Asp-39, His-69 and Cys-73 at position 1 and with His-72, Cys-73, Met-225 and Wat-324 at position 2. The Hg(II) with an occupancy of 0.80 at position 1 perturbs and stereochemistry of the residues of the catalytic triad Asp-39, His-69 and Ser-224 appreciably thus reducing the enzymatic activity of proteinase K to approximately 15/100.