Analysis of inter-subunit contacts reveals the structural malleability of extracellular domains in platelet glycoprotein Ib-IX complex.

ABSTRACT: The glycoprotein (GP)Ib-IX complex is critical to hemostasis and thrombosis. Its proper assembly is closely correlated with its surface expression level and requires cooperative interactions among extracellular and transmembrane domains of Ib?, Ib? and IX subunits. Two interfaces have been previously identified between the extracellular domains of Ib? and IX.To understand how extracellular domains interact in GPIb-IX.The Ib? extracellular domain (Ib?E ) or the IX counterpart (IXE ) in GPIb-IX was replaced with a well-folded Ib?E /IXE chimera called Ib?Eabc , and the effect of domain replacement on assembly and expression of the receptor complex in transiently transfected Chinese hamster ovary cells was analyzed.Replacing IXE with Ib?Eabc in GPIb-IX retained interface 1 but not interface 2 between the extracellular domains. While this domain replacement preserved complex integrity, the expression levels of Ib? and Ib? were significantly reduced. Additional domain replacement with Ib?Eabc or Ib?E in GPIb-IX produced the complex at disparate expression levels that cannot be simply explained by two separate interfaces. In particular, when Ib?E in GPIb-IX was replaced by Ib?Eabc , Ib? and IX were expressed at approximately 70% of the wild-type level. Their levels were not reduced when IXE was changed further to Ib?E .Our results demonstrate the importance of the association between Ib? and IX extracellular domains for complex assembly and efficient expression, and provide evidence for the structural malleability of these domains that may accommodate and propagate conformational changes therein.

SUBMITTER: Zhou L 

PROVIDER: S-EPMC4137403 | biostudies-literature | 2014 Jan

REPOSITORIES: biostudies-literature