The decameric structure of bovine pancreatic trypsin inhibitor (BPTI) crystallized from thiocyanate at 2.7 Å resolution

International audienceThe structure of a monoclinic form of bovine pancreatic trypsin inhibitor (BPTI) crystallized from a thiocyanate solution has been determined and refined at 2.7 Å resolution. The space group is P2$_1$ with $a$ = 71.56, $b$ = 73.83, $c$ = 64.47 Å, $\beta$ = 93.9° and Z = 20. The ten independent molecules were located by a multi-body molecular-replacement search as developed in the AMoRe program, starting from a single monomer model (PDB code: 6PTI). The molecular arrangement of the subunits is a decamer resulting from the combination of two orthogonal fivefold and twofold non-crystallographic axes. This builds a globular micelle-like particle which minimizes hydrophobic interactions with the solvent. The refinement was conducted with non-crystallographic symmetry constraints up to a final residual of R = 0.20 (R$_{free}$ = 0.26). The root-mean-square deviations from ideal geometry were 0.015 Å and 1.6° on bond distances and bond angles, respectively. Several sites for thiocyanate ions were analyze