CDNA CLONING, TISSUE DISTRIBUTION, AND IDENTIFICATION OF THE CATALYTIC TRIAD OF MONOGLYCERIDE LIPASE - EVOLUTIONARY RELATIONSHIP TO ESTERASES, LYSOPHOSPHOLIPASES, AND HALOPEROXIDASES

Monoglyceride lipase catalyzes the last step in the hydrolysis of stor ed triglycerides in the adipocyte and presumably also complements the action of lipoprotein lipase in degrading triglycerides from chylomicr ons and very low density lipoproteins. Monoglyceride Lipase was cloned from a mouse adipocyte cDNA library. The predicted amino acid sequenc e consisted of 302 amino acids, corresponding to a molecular weight. o f 33,218, The sequence showed no extensive homology to other known mam malian proteins, but a number of microbial proteins, including two bac terial lysophospholipases and a family of haloperoxidases, were found to be distantly related to this enzyme, By means of multiple sequence alignment and secondary structure prediction, the structural elements in monoglyceride lipase, as well as the putative catalytic triad, were identified, The residues of the proposed triad, Ser-122, in a GXSXG m otif, Asp-239, and His-269, were confirmed by site-directed mutagenesi s experiments. Northern blot analysis revealed that monoglyceride lipa se is ubiquitously expressed among tissues, with a transcript size of about 4 kilobases.