title: The snake venom protein botrocetin acts as a biological brace to promote dysfunctional platelet aggregation.
abstract: Botrocetin is a snake venom protein that enhances the affinity of the A1 domain of plasma von Willebrand factor (vWF) for the platelet receptor glycoprotein Ibalpha (GPIbalpha), an event that contributes to bleeding and host death. Here we describe a kinetic and crystallographic analysis of this interaction that reveals a novel mechanism of affinity enhancement. Using high-temporal-resolution microscopy, we show that botrocetin decreases the GPIbalpha off-rate two-fold in both human and mouse complexes without affecting the on-rate. The key to this behavior is that, upon binding of GPIbalpha to vWF-A1, botrocetin prebound to vWF-A1 makes no contacts initially with GPIbalpha, but subsequently slides around the A1 surface to form a new interface. This two-step mechanism and flexible coupling may prevent adverse alterations in on-rate of GPIbalpha for vWF-A1, and permit adaptation to structural differences in GPIbalpha and vWF in several prey species.
authors.affiliation: Infectious and Inflammatory Disease Center, The Burnham Institute, 10901 North Torrey Pines Road, La Jolla, California 92037, USA.
authors.forename: Koichi
authors.initials: K
authors.lastname: Fukuda
authors.forename: Teresa
authors.initials: T
authors.lastname: Doggett
authors.forename: Ian J
authors.initials: IJ
authors.lastname: Laurenzi
authors.forename: Robert C
authors.initials: RC
authors.lastname: Liddington
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Diacovo
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001792:Blood Platelets / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D003435:Crotalid Venoms / Q000737:chemistry / Q000494:pharmacology*; D018360:Crystallography, X-Ray; D006801:Humans; D007700:Kinetics; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010973:Platelet Adhesiveness; D010974:Platelet Aggregation / Q000187:drug effects*; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D014841:von Willebrand Factor / Q000737:chemistry / Q000378:metabolism
chemical_list: D003435:Crotalid Venoms; D019038:Platelet Glycoprotein GPIb-IX Complex; D014841:von Willebrand Factor; C030961:botrocetin