Crystallization and preliminary X-ray crystallographic studies of a psychrophilic subtilisin-like protease Apa1 from Antarctic Pseudoalteromonas sp. strain AS-11

The psychrophilic alkaline serine protease Apa1 secreted by the Antarctic psychrotroph Pseudoalteromonas sp. strain AS-11 consists of a subtilisin-like region (293 residues) and an additional insert region (148 residues) that does not show a sequence homology to any proteins in the RCSB Protein Data Bank. Apa1 inhibited with phenylmethanesulfonyl fluoride has been crystallized and X-ray diffraction data have been collected to 1.78 Å resolution. The crystals belong to space group C2, with unit-cell parameters a = 122.94, b = 138.48, c = 64.77 Å, α = γ = 90, β = 97.5°. A molecular-replacement solution has been found using the structure of the mesophilic counterpart subtilisin DY with 38% sequence identity to the catalytic domain of Apa1 as a search model. This is the first crystallographic study of a cold-adapted subtilisin-like protease.