MOLECULAR-STRUCTURE OF CRYSTALLINE STREPTOMYCES-GRISEUS PROTEASE-A AT 2.8-A RESOLUTION .1. CRYSTALLIZATION, DATA-COLLECTION AND STRUCTURAL-ANALYSIS

Excellent tetragonal crystals of the A protease from Streptomyces griseus were grown by equilibrium dialysis from 1.3 m-NaH2PO4 at pH 4.1. There are four molecules in the unit cell (axial lengths a = b = 55.14(4) A ̊, and c = 54.81(3) A ̊); the space group is P42. Intensity data were collected on a Picker FACS-1 diffractometer to minimum d spacings of 2.8 Å for crystals of the native enzyme and four heavy-atom derivatives. Background corrections to the measured peak intensities were made by a least-squares fit to a multi-dimensional function of the net intensity (I) and a linear combination of 2θ and φ. There was no dependence of the background on χ. The phase determination process has resulted in an overall average flgure-of-merit of 0.82 for 3957 reflections. The overall ratio of the root-mean-square (r.m.s.) heavy-atom scattering factor to the r.m.s. lack-of-closure errors for the derivatives ranged from 1.53 to 3.64. The common sodium mersalyl and mercury chloranilate site was close to the imidazole ring of His57; the rhenium site was located in a pocket between two enzyme molecules. The r.m.s. deviation of the measured co-ordinates to a stereochemically fitted model was 0.25 Å for the 1265 non-hydrogen atoms of the A protease. © 1978.