RT Journal Article
SR Electronic
T1 A transient amphipathic helix in PCSK9’s prodomain facilitates low-density lipoprotein binding
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 743195
DO 10.1101/743195
A1 Samantha K. Sarkar
A1 Alexander C.Y. Foo
A1 Angela Matyas
A1 Tanja Kosenko
A1 Natalie K. Goto
A1 Ariela Vergara-Jaque
A1 Thomas A. Lagace
YR 2019
UL http://biorxiv.org/content/early/2019/08/22/743195.abstract
AB Proprotein convertase subtilisin/kexin type-9 (PCSK9) is a ligand of low-density lipoprotein receptor (LDLR) that promotes LDLR degradation in late endosomes/lysosomes. In human plasma, 30-40% of PCSK9 is bound to LDL particles; however, the physiological significance of this interaction remains unknown. LDL binding in vitro requires a disordered N-terminal region in PCSK9’s prodomain. Here we report that peptides corresponding to a predicted amphipathic α-helix in the prodomain N-terminus adopted helical structure in a membrane-mimetic environment; this effect was greatly enhanced by an R46L substitution representing an athero-protective PCSK9 loss-of-function mutation. A helix-disrupting proline substitution within the putative α-helical motif in full-length PCSK9 lowered LDL binding affinity >5-fold. Modeling studies suggested the transient α-helix aligns multiple polar residues to interact with positive-charged residues in the C-terminal domain. Gain-of-function PCSK9 mutations associated with familial hypercholesterolemia (FH) and clustered at the predicted interdomain interface (R469W, R496W, F515L) inhibited LDL binding, which was abolished for the R496W variant. These studies inform on allosteric conformational changes in PCSK9 required for high-affinity binding to LDL particles. Moreover, we report the initial identification of FH-associated mutations that diminish the ability of PCSK9 to bind LDL, supporting that LDL association in the circulation inhibits PCSK9 activity.