Structure determination and refinement of benzamidine-inhibited trypsin from the North Atlantic salmon (Salmo salar) at 1.82 Å resolution

The structure of the serine protease trypsin from the North Atlantic salmon (Salmo salar) has been solved by molecular replacement and refined by restrained least-squares methods to a conventional R factor of 16.4% using diffractometer data in the 6.0–1.82 Å resolution range (14 443 reflections greater than 3σ). The model comprises 1793 protein atoms and 180 solvent molecules which were given unit occupancies, and the average temperature factors for protein atoms and solvent oxygen atoms are 15.2 and 36.8 Ų, respectively. The estimated error in atomic positions is about 0.2 Å. The structure of salmon trypsin was solved and refined with only a small part of the amino-acid sequence known. However, a gene sequence of salmon trypsin has later become available. Some discrepancies between this sequence and the sequence obtained from the present X-ray crystal study indicate that the mentioned sequences may correspond to isoenzymes. The structure of salmon trypsin is similar to other trypsins of known structure.