Stereoselectivity of microbial lipases. The substitution at position sn-2 of triacylglycerol analogs influences the stereoselectivity of different microbial lipases.

In the present study, the stereoselectivity of purified lipases from Candida rugosa, Chromobacterium viscosum, Pseudomonas species and Rhizopus arrhizus towards triacylglycerols in comparison to various structural analogs were investigated. Different triacylglycerol analogs with distinct polarities at position sn-2 of the glycerol backbone (1,3-diacy1-2-X-glycerol, where 2-X = 2-acyloxy, 2-alkyloxy, 2-deoxy-2-alkyl, or 2-deoxy-2-phenyl) were synthesized. Substrate hydrophobicity and steric requirement was modified by variation of the alkyl and acyl chain length. Hydrolysis of these substrates demonstrated that minor structural variations at C2 of triacylglycerol strongly affect the stereoselectivity of the lipases tested. It was noteworthy that the variation of substrate structure did not only affect the quantity of stereoselectivity expressed as percentage enantiomeric excess, but also resulted in a reversal of stereo-preference in some cases. Replacement of the acylester in position 2 of glycerol by a non-ester-linked aliphatic moiety shifted the preference of Chromobacterium viscosum lipase from sn-3 to sn-1. Lipases from Chromobacterium viscosum, Pseudomonas species and Rhizopus arrhizus exhibited sn-3 preference with 2-deoxy-2-phenyl analogs, while towards substrates with a 2-deoxy-2-alkyl moiety sn-1 stereobias was recorded. Candida rugosa lipase was rather insensitive to substrate variations concerning the polarity at position 2 of the glycerol backbone. However, variation of the acyl chain length significantly influenced stereoselectivity of this lipase.