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J. Biol. Chem., Vol. 281, Issue 20, 13931-13938, May 19, 2006

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Interaction of Lipoprotein Lipase and Receptor-associated Protein^*

From the Division of Nutritional Sciences, Cornell University, Ithaca, New York 14853

Receptor-associated protein (RAP) is a recognized chaperone/escort protein for members of the low density lipoprotein receptor family. In this report, we show that RAP binds to lipoprotein lipase (LPL) and may play a role in the maturation of LPL. Binding of highly purified RAP to LPL was demonstrated in vitro by solid phase assays, surface plasmon resonance, and rate zonal centrifugation. The dissociation constant for this interaction measured by the first two techniques ranged between 2.4 and 13 nM, values similar to those reported for the binding of RAP to LRP or gp330. The specificity of the interaction was demonstrated by competition with a panel of LPL monoclonal antibodies. Rate zonal centrifugation demonstrated the presence of a stable complex with an apparent M_r consistent with the formation of a complex between monomeric LPL and RAP. RAP·LPL complexes were co-immunoprecipitated in adipocyte lysates or from solutions of purified LPL and RAP. The interaction was also demonstrated in whole cells by cross-linking experiments. RAP-deficient adipocytes secreted LPL with a specific activity 2.5-fold lower than the lipase secreted by control cells. Heparin addition to cultured RAP-deficient adipocytes failed to stimulate LPL secretion in the medium, suggesting defective binding of the lipase to the plasma membrane. These studies demonstrate that RAP binds to LPL with high affinity both in purified systems and cell extracts and that RAP-deficient adipocytes secrete poorly assembled LPL. A function of RAP may be to prevent premature interaction of LPL with binding partners in the secretory pathway, namely LRP and heparan sulfate proteoglycan.

Received for publication, February 1, 2006 , and in revised form, March 1, 2006.

^* This work was supported by National Institutes of Health Grants HL14990 and DK7158 and internal grant funds from Nutritional Sciences, Cornell University. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Present address: University of Maine at Machias, 9 O'Brien Ave., Machias, ME 04654.

² To whom correspondence should be addressed: 321 Savage Hall, Division of Nutritional Sciences, Cornell University, Ithaca, NY 14853. Tel.: 607-255-1927; Fax: 607-255-1033; E-mail: ab55{at}cornell.edu.

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