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Journal of Lipid Research, Vol. 44, 1306-1314, July 2003
Copyright © 2003 by American Society for Biochemistry and Molecular Biology

The amino acid sequences of the carboxyl termini of human and mouse hepatic lipase influence cell surface association

Robert J. Brown^*,, Joshua R. Schultz^*,,, Kerry W. S. Ko^*, John S. Hill^**, Tanya A. Ramsamy^*,, Ann L. White, Daniel L. Sparks^*,, and Zemin Yao^1,*,,

^* Lipoprotein and Atherosclerosis Research Group, University of Ottawa, Ottawa, Canada
University of Ottawa Heart Institute, Department of Biochemistry, Microbiology, & Immunology, University of Ottawa, Ottawa, Canada
Department of Pathology & Laboratory Medicine, University of Ottawa, Ottawa, Canada
^** Department of Pathology & Laboratory Medicine, University of British Columbia, Vancouver, Canada
Department of Clinical Nutrition, The University of Texas Southwestern Medical Center, Dallas, TX 75390

¹ To whom correspondence should be addressed. e-mail: zyao{at}ottawaheart.ca

Human hepatic lipase (hHL) mainly exists cell surface bound, whereas mouse HL (mHL) circulates in the blood stream. Studies have suggested that the carboxyl terminus of HL mediates cell surface binding. We prepared recombinant hHL, mHL, and chimeric proteins (hHLmt and mHLht) in which the carboxyl terminal 70 amino acids of hHL were exchanged with the corresponding sequence from mHL. The hHL, mHL, and hHLmt proteins were catalytically active using triolein and tributyrin as substrates. In transfected cells, the majority of hHLs bound to the cell surface, with only 4% of total extracellular hHL released into heparin-free media, whereas under the same conditions, 61% of total extracellular mHLs were released. Like mHL, hHLmt showed decreased cell surface binding, with 68% of total extracellular hHLmt released. To determine the precise amino acid residues involved in cell surface binding, we prepared a truncated hHL mutant (hHL₄₇₁) by deleting the carboxyl terminal five residues (KRKIR). The hHL₄₇₁ also retained hydrolytic activity with triolein and tributyrin, and showed decreased cell surface binding, with 40% of total extracellular protein released into the heparin-free media.

These data suggest that the determinants of cell surface binding exist within the carboxyl terminal 70 amino acids of hHL, of which the last five residues play an important role.

Abbreviations: HBD, heparin binding domain; hHL, human hepatic lipase; HSPG, heparan sulfate proteoglycan; LPL, lipoprotein lipase; LRP, LDL receptor-related protein; mHL, mouse hepatic lipase; TG, triacylglycerol

Supplementary key words lipolysis • heparin • heparin binding domain • heparan sulfate proteoglycan • tributyrin • triolein

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