Electrostatic effects play a central role in cold adaptation of trypsin

Organisms that live in constantly cold environments have to adapt their met abolism Co low temperatures, but mechanisms of enzymatic adaptation to cold environments are not fully understood. Cold active trypsin catalyses react ions more efficiently and binds ligands more strongly in comparison to warm active trypsin. We have addressed this issue by means of comparative free energy calculations studying the binding of positively charged ligands to t wo trypsin homologues. Stronger inhibition of the cold active trypsin by be nzamidine and positively charged P1-variants of BPTI is caused by rather su btle electrostatic effects. The different affinity of benzamidine originate s solely from long range interactions, while the increased binding of P1-Ly s and -Arg variants of BPTI is attributed to both long and short range effe cts that are enhanced in the cold active trypsin compared to the warm activ e counterpart, Electrostatic interactions thus provide an efficient strateg y for cold adaptation of trypsin. (C) 2001 Federation of European Biochemic al Societies. Published by Elsevier Science B,V, All rights reserved.