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Papers In Press, published online ahead of print September 1, 2004
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Cell & Developmental Biology, Univ. of Penna. School of Medicine, Philadelphia, PA 19104
Corresponding Author: glickj{at}mail.med.upenn.edu
Human endothelial lipase (EL), a member of the triglyceride lipase gene family, has five potential N-linked glycosylation sites, two of which are conserved in both lipoprotein lipase and hepatic lipase. Reduction in molecular weight of EL after treatment with glycosidases and after treatment of EL-expressing cells with the glycosylation inhibitor tunicamycin, demonstrated that EL is a glycosylated protein. Each putative glycosylation site was examined by site-directed mutagenesis of the asparagine (Asn). Mutation of Asn60 markedly reduced secretion and slightly increased specific activity. Mutation of Asn116 did not influence secretion, but increased specific activity. In both cases this resulted from decreased apparent Km and increased apparent Vmax. Mutation of Asn373 did not influence secretion but significantly reduced specific activity, due to a decrease in apparent Vmax. Mutation of Asn471 resulted in no reduction in secretion or specific activity. Mutation of Asn449 resulted in no change in secretion, activity, or molecular weight, indicating that the site is not utilized. The ability of mutants secreted at normal levels to mediate bridging between LDL and cell surfaces was examined. The Asn373 mutant demonstrated a three-fold decrease in bridging compared to wild-type EL, while Asn116 and Asn471 were similar to wild-type EL.
Revised on August 18, 2004
Accepted on August 19, 2004
Role of N-linked glycosylation in the secretion and activity of endothelial lipase
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