Self-Association of Human PCSK9 Correlates with Its LDLR-Degrading Activity

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• 作者：Daping Fan ; Patricia G. Yancey ; Shenfeng Qiu ; Lei Ding ; Edwin J. Weeber ; MacRae F. Linton ; Sergio Fazio
• 刊名：Biochemistry
• 出版年：2008
• 出版时间：February 12, 2008
• 年：2008
• 卷：47
• 期：6
• 页码：1631 - 1639
• 全文大小：396K
• 年卷期：v.47,no.6(February 12, 2008)
• ISSN：1520-4995

文摘

Genetic studies have demonstrated an important role for proprotein convertase subtilisin/kexintype 9 (PCSK9) as a determinant of plasma cholesterol levels. However, the underlying molecularmechanism is not completely understood. To this end, we have generated a mammalian cell expressionsystem for human PCSK9 and its mutants and produced transgenic mice expressing human PCSK9.HEK293T cells transfected with the human PCSK9 DNA construct expressed and secreted PCSK9 anddisplayed decreased LDLR levels; functional PCSK9 protein was purified from the conditioned medium.In vitro studies showed that PCSK9 self-associated in a concentration-, temperature-, and pH-dependentmanner. A mixture of PCSK9 monomers, dimers, and trimers displayed an enhanced LDLR degradingactivity compared to monomeric PCSK9. A gain-of-function mutant, D374Y, displayed greatly increasedself-association compared to wild-type PCSK9. Moreover, we demonstrated that the catalytic domain ofPCSK9 is responsible for the self-association. Self-association of PCSK9 was enhanced by incubationwith mouse apoE^-/- VLDL and inhibited by incubation with both human and mouse HDL. When PCSK9protein was incubated with total serum, it partially associated with LDL and HDL but not with VLDL.In transgenic mice, PCSK9 also associated with LDL and HDL but not with VLDL. We conclude thatself-association is an intrinsic property of PCSK9, correlated to its LDLR-degrading activity and affectedby plasma lipoproteins. These results provide a basis for developing strategies to manipulate PCSK9activity in the circulation for the treatment of hypercholesterolemia.