Psychrophilics yeasts: new biocatalytic agents for enoate reductase activities

Owing to widespread diffusion of areas characterized by permanent low temperatures (e.g. deep-sea waters, mountains and polar regions), psychrophilic microorganisms have the largest terrestrial distribution. Adaptation of microbial life at low temperatures requires some changes, mainly at the level of cell membrane components (including transport systems), proteins and nucleic acids.Psychrophilic organisms produce enzymes functioning in coldenvironment and simply denaturing at high temperature. Suchcold-active enzymes have a more flexible structure to undergo the conformational changes necessary for catalysis with a lower energy demand. Owing to their high catalytic activity at low temperatures, low thermostability and unusual specificities, cold-active enzymes offer novel opportunities for biotechnological exploitation.The enormous potential of biocatalysts for the production of enantiopure products of industrial interest remains to beexploited, especially in the area of enantioselective alkene reductions, due to their marked regio- and stereo-selectivity. One of the emerging reductive chemistry is the asymmetric reductionof alpha,beta-unsaturated carbonyl compounds through microbialwhole-cells rich in enoate reductase (ER), a flavin-dependentenzyme belonging to the ‘old yellow enzyme’ (OYE) family.Even though massive screenings for yeasts as reducing catalystshave been carried out so far, there is still a need for new biocatalysts able to performing highly stereoselective reactions. Consequently, the potential of yeast biocatalysis appears to be still far from being fully explored. In this study we report the results of a screening on facultative psychrophilic yeasts (belonging to the species Cryptococcus gilvescens and Cryptococcus gastricus) for new cold-adapted enoate reductases using (4S)-(+)-carvone as a model substrate. The preliminary results obtained using growing cells demonstrate that the ERs activities are apparently expressed to a greater extent inpsychrophilic yeasts with respect to the mesophilic ones. In particular, C. gastricus exhibited the better biocatalytic performances.The results obtained by using other catalytic forms (resting orlyophilized cells) will be presented.