Structure of native pancreatic elastase from North Atlantic salmon at 1.61 Å resolution

The crystal structure of native salmon pancreatic elastase (SPE) has been solved by molecular-replacement methods, and refined by conventional conjugate-gradient methods and simulated-annealing techniques. The final R value is 17.2% for 21 389 reflections between 8.0 and 1.61 Å, and the corresponding free R value is 23.9%. The overall tertiary structure of SPE is remarkably similar to that of porcine pancreatic elastase I (PPE), to which it shows about 67% sequence identity. The primary structure of SPE is determined from the electron-density maps, and only about 15 side chains are somewhat uncertain. Interesting differences between SPE and PPE, are one sequence deletion assigned to position 186, the residue 192 at the entrance of the specificity pocket is substituted from a Gln in PPE to Asn in SPE, and one of the calcium ligands is different. Furthermore, electron density is missing in SPE for the last three residues of the C-terminal helix. A comparison of the present amino-acid sequence of SPE with other sequences available indicates that SPE belongs to the class 1 pancreatic elastases.