Bacterial biocatalysts: Molecular biology, three-dimensional structures, and biotechnological applications of lipases

Bacteria produce and secrete lipases, which can catalyze both the hydrolysi s and the synthesis of long-chain acylglycerols. These reactions usually pr oceed with high regioselectivity and enantioselectivity, and, therefore, Li pases have become very important stereoselective biocatalysts used in organ ic chemistry. High-level production of these biocatalysts requires the unde rstanding of the mechanisms underlying gene expression, folding, and secret ion. Transcription of Lipase genes may be regulated by quorum sensing and t wo-component systems; secretion can proceed either via the Sec-dependent ge neral secretory pathway or via ABC transporters. In addition, some lipases need folding catalysts such as the lipase-specific foldases and disulfide-b ond-forming proteins to achieve a secretion-competent conformation. Three-d imensional structures of bacterial lipases were solved to understand the ca talytic mechanism of lipase reactions. Structural characteristics include a n alpha/beta hydrolase fold, a catalytic triad consisting of a nucleophilic serine located in a highly conserved Gly-X-Ser-X-Gly pentapeptide, and an aspartate or glutamate residue that is hydrogen bonded to a histidine. Four substrate binding pockets were identified for triglycerides: an oxyanion h ole and three pockets accommodating the fatty acids bound at positions sn-1 , sn-2, and sn-3. The differences in size and the hydrophilicity/hydrophobi city of these pockets determine the enantiopreference of a lipase. The unde rstanding of structure-function relationships will enable researchers to ta ilor new lipases for biotechnological applications. At the same time, direc ted evolution in combination with appropriate screening systems will be use d extensively as a novel approach to develop lipases with high stability an d enantioselectivity.