Interaction between the ligand-binding domain of the LDL receptor and the C-terminal domain of PCSK9 is required for PCSK9 to remain bound to the LDL receptor during endosomal acidification

• Published in: Human molecular genetics 2012-03, Vol.21 (6), p.1402-1409
• Main Authors: TVETEN, Kristian, HOLLA, Øystein L, CAMERON, Jamie, BISMO STRØM, Thea, ERIK BERGE, Knut, LAERDAHL, Jon K, LEREN, Trond P
• Format: Article
• Language: English
• Subjects: Acids - metabolism; Animals; Biological and medical sciences; Blotting, Western; Cell Membrane - metabolism; Cell receptors; Cell structures and functions; Cells, Cultured; CHO Cells; Cricetinae; Endosomes - metabolism; Fundamental and applied biological sciences. Psychology; Genetics of eukaryotes. Biological and molecular evolution; Humans; Hydrogen-Ion Concentration; Kidney - cytology; Kidney - metabolism; Lysosomes - metabolism; Miscellaneous; Molecular and cellular biology; Mutagenesis, Site-Directed; Mutation - genetics; Proprotein Convertase 9; Proprotein Convertases - genetics; Proprotein Convertases - metabolism; Protein Binding; Protein Structure, Tertiary; Protein Transport; Receptors, LDL - genetics; Receptors, LDL - metabolism; Serine Endopeptidases - genetics; Serine Endopeptidases - metabolism; Signal Transduction
• ISSN: 0964-6906; 1460-2083
• DOI: 10.1093/hmg/ddr578

Proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to the epidermal growth factor homology domain repeat A of the low-density lipoprotein receptor (LDLR) at the cell surface and disrupts recycling of the internalized LDLR. As a consequence, the LDLR is rerouted to the lysosomes for degradation. Although PCSK9 may bind to an LDLR lacking the ligand-binding domain, at least three ligand-binding repeats of the ligand-binding domain are required for PCSK9 to reroute the LDLR to the lysosomes. In this study, we have studied the binding of PCSK9 to an LDLR with or without the ligand-binding domain at increasingly acidic conditions in order to mimic the milieu of the LDLR:PCSK9 complex as it translocates from the cell membrane to the sorting endosomes. These studies have shown that PCSK9 is rapidly released from an LDLR lacking the ligand-binding domain at pH in the range of 6.9-6.1. A similar pattern of release at acidic pH was also observed for the binding to the normal LDLR of mutant PCSK9 lacking the C-terminal domain. Together these data indicate that an interaction between the negatively charged ligand-binding domain of the LDLR and the positively charged C-terminal domain of PCSK9 is required for PCSK9 to remain bound to the LDLR during the early phase of endosomal acidification as the LDLR translocates from the cell membrane to the sorting endosome.