COLD ADAPTION OF ENZYMES - STRUCTURAL COMPARISON BETWEEN SALMON AND BOVINE TRYPSINS

The crystal structure of an anionic form of salmon trypsin has been de termined at 1.82 Angstrom resolution. We report the first structure of a trypsin from a phoikilothermic organism in a detailed comparison to mammalian trypsins in order to look for structural rationalizations f or the cold-adaption features of salmon trypsin. This form of salmon t rypsin (ST II) comprises 222 residues, and is homologous to bovine try psin (BT) in about 65% of the primary structure. The tertiary structur es are similar, with an overall displacement in main chain atomic posi tions between salmon trypsin and various crystal structures of bovine trypsin of about 0.8 Angstrom. Intramolecular hydrogen bonds and hydro phobic interactions are compared and discussed in order to estimate po ssible differences in molecular flexibility which might explain the hi gher catalytic efficiency and lower thermostability of salmon trypsin compared to bovine trypsin. No overall differences in intramolecular i nteractions are detected between the two structures, but there are dif ferences in certain regions of the structures which may explain some o f the observed differences in physical properties. The distribution of charged residues is different in the two trypsins, and the impact thi s might have on substrate affinity has been discussed. (C) 1994 Wiley- Liss, Inc.