The Transmembrane Domains of ? and IX Subunits Mediate the Localization of the Platelet Glycoprotein Ib-IX Complex to the Glycosphingolipid-enriched Membrane Domain.

ABSTRACT: We have previously reported that the structural elements of the GP Ib-IX complex required for its localization to glycosphingolipid-enriched membranes (GEMs) reside in the Ib? and IX subunits. To identify them, we generated a series of cell lines expressing mutant GP Ib? and GP IX where 1) the cytoplasmic tails (CTs) of either or both GP Ib? and IX are truncated, and 2) the transmembrane domains (TMDs) of GP Ib? and GP IX were swapped with the TMD of a non-GEMs associating molecule, human transferrin receptor. Sucrose density fractionation analysis showed that the removal of either or both of the CTs from GP Ib? and GP IX does not alter GP Ib?-GEMs association when compared with the wild type. In contrast, swapping of the TMDs of either GP Ib? or GP IX with that of transferrin receptor results in a significant loss (? 50%) of GP Ib? from the low density GEMs fractions, with the largest effect seen in the dual TMD-replaced cells (> 80% loss) when compared with the wild type cells (100% of GP Ib? present in the GEMs fractions). Under high shear flow, the TMD-swapped cells adhere poorly to a von Willebrand factor-immobilized surface to a much lesser extent than the previously reported disulfide linkage dysfunctional GP Ib?-expressing cells. Thus, our data demonstrate that the bundle of GP Ib? and GP IX TMDs instead of their individual CTs is the structural element that mediates the ?/IX complex localization to the membrane GEMs, which through the ?/? disulfide linkage brings GP Ib? into the GEMs.

SUBMITTER: Xu G 

PROVIDER: S-EPMC4571966 | biostudies-literature | 2015 Sep

REPOSITORIES: biostudies-literature