THE STRUCTURE OF BOVINE PANCREATIC TRYPSIN INHIBITOR AT 125K: DEFINITION OF CARBOXYL-TERMINAL RESIDUES GLYCINE-57 AND ALANINE-58
SIDE CHAINS OF RESIDUES GLU 7 AND ARG 53 WERE FOUND TO OCCUPY TWO MAJOR SITES. THESE ARE DENOTED BY THE ALTERNATE SITE INDICATORS *A* AND *B*.
Structure of bovine pancreatic trypsin inhibitor at 125 K definition of carboxyl-terminal residues Gly57 and Ala58.
INITIAL MODEL DERIVED FROM THE COORDINATE SET OF PDB ENTRY 5PTI. PRIOR TO REFINEMENT THE MODEL WAS MODIFIED AS FOLLOWS: (I) DISORDER WAS REMOVED, MAJOR CONFORMATIONS INCLUDED AT FULL OCCUPANCY. (II) HYDROGEN ATOMS REMOVED. (III) ISOTROPIC THERMAL PARAMETERS HALVED, CONVERTED TO *U* FORMAT AND ROUNDED TO THE NEAREST 0.01 ANGSTROM SQUARED. (IV) AMINO ACID GEOMETRIES RESTRAINED ACCORDING TO ENGH AND HUBER (1991), ACTA CRYST. A47 PP.392-400.
RESIDUES GLU 7 AND ARG 53 WERE MODELED IN TWO CONFORMATIONS. 145.6 WATER MOLECULES OVER 167 SITES WERE MODELED. 123 ARE AT FULL OCCUPANCY, 39 ARE AT HALF OCCUPANCY AND THE REMAINDER HAVE OCCUPANCIES DETERMINED BY THE DISORDER AT RESIDUES GLU 7 AND ARG 53. THE PHOSPHATE WAS MODELED IN TWO CONFORMATIONS. RESTRAINED ANISOTROPIC THERMAL PARAMETERS WERE REFINED. THE COORDINATES IN THIS ENTRY ARE THOSE OF THE ISOTROPIC MODEL. R VALUES FOR THE ISOTROPIC AND ANISOTROPIC MODELS WERE 0.187 AND 0.161 FOR ALL DATA. FREE R VALUES FOR BOTH MODELS WERE INSIGNIFICANTLY DIFFERENT. PROTEIN GEOMETRY FOR MAJOR AND MINOR CONFORMATIONS OF GLU 7 AND ASP 53 WAS CHECKED WITH THE PROCHECK PROGRAM (LASKOWSKI, MACARTHUR, MOSS, THORNTON (1993) J. APPL. CRYST. 26, 283 - 291). THE OMEGA TORSION ANGLE OF ARG 1 SHOWS A MARKED DEVIATION FROM PLANARITY. ELECTRON DENSITY MAPS CLEARLY SUPPORT THIS DISTORTION.
BOVINE PANCREATIC TRYPSIN INHIBITOR (BPTI) (CRYSTAL FORM II)
MKMSRLCLSVALLVLLGTLAASTPGCDTSNQAKAQRPDFCLEPPYTGPCKARIIRYFYNAKAGLCQTFVYGGCRAKRNNF KSAEDCMRTCGGAIGPWENL