The Transmembrane Domain of Glycoprotein Ibβ Is Critical to Efficient Expression of Glycoprotein Ib-IX Complex in the Plasma Membrane

Abstract

Lack of expression of glycoprotein (GP) Ib-IX-V complex in platelets often results from mutations in its three subunits: GP Ibα, GP Ibβ, or GP IX. The requirement of all three subunits in the efficient surface expression of the receptor complex has been reproduced in Chinese hamster ovary cells. Here, we probed the role of the transmembrane domains in expression of the GP Ib-IX complex and potential interactions between these domains. Replacing the transmembrane domains of either GP Ibα or GP Ibβ, but not that of GP IX, with unrelated sequences markedly diminished surface expression of the GP Ib-IX complex in transiently transfected Chinese hamster ovary cells. Replacement of the Ibβ transmembrane domain produced the largest effect. Furthermore, several single-site mutations in the Ibβ transmembrane domain were found to significantly decrease overall expression as well as surface expression of GP Ibα, probably by perturbing the interaction between the Ibα and Ibβ transmembrane domains and in turn reducing the stability of GP Ibα in the cell. Mutations S503V and S503L in the Ibα transmembrane domain partly reversed the expression-decreasing effect of mutation H139L, but not the others, in the Ibβ transmembrane domain, suggesting a specific interaction between these two polar residues. Together, our results have demonstrated the importance of the Ibβ transmembrane domain, through its interaction with the Ibα counterpart, to the proper assembly and efficient surface expression of the GP Ib-IX complex. Lack of expression of glycoprotein (GP) Ib-IX-V complex in platelets often results from mutations in its three subunits: GP Ibα, GP Ibβ, or GP IX. The requirement of all three subunits in the efficient surface expression of the receptor complex has been reproduced in Chinese hamster ovary cells. Here, we probed the role of the transmembrane domains in expression of the GP Ib-IX complex and potential interactions between these domains. Replacing the transmembrane domains of either GP Ibα or GP Ibβ, but not that of GP IX, with unrelated sequences markedly diminished surface expression of the GP Ib-IX complex in transiently transfected Chinese hamster ovary cells. Replacement of the Ibβ transmembrane domain produced the largest effect. Furthermore, several single-site mutations in the Ibβ transmembrane domain were found to significantly decrease overall expression as well as surface expression of GP Ibα, probably by perturbing the interaction between the Ibα and Ibβ transmembrane domains and in turn reducing the stability of GP Ibα in the cell. Mutations S503V and S503L in the Ibα transmembrane domain partly reversed the expression-decreasing effect of mutation H139L, but not the others, in the Ibβ transmembrane domain, suggesting a specific interaction between these two polar residues. Together, our results have demonstrated the importance of the Ibβ transmembrane domain, through its interaction with the Ibα counterpart, to the proper assembly and efficient surface expression of the GP Ib-IX complex. Platelet glycoprotein (GP) 2The abbreviations used are: GP, glycoprotein; pL, poly-Leu; pLA, poly-Leu-Ala; TM, transmembrane; vWF, von Willebrand factor; CHO, Chinese hamster ovary; PBS, phosphate-buffered saline; BSA, bovine serum albumin.2The abbreviations used are: GP, glycoprotein; pL, poly-Leu; pLA, poly-Leu-Ala; TM, transmembrane; vWF, von Willebrand factor; CHO, Chinese hamster ovary; PBS, phosphate-buffered saline; BSA, bovine serum albumin. Ib-IX-V complex mediates the initial tethering and rolling of platelets on von Willebrand factor (vWF) localized at the vascular injury site (1Lopez J.A. Blood Coagul. Fibrinolysis. 1994; 5: 97-119Crossref PubMed Scopus (291) Google Scholar, 2Berndt M.C. Shen Y. Dopheide S.M. Gardiner E.E. Andrews R.K. Thromb. Haemost. 2001; 86: 178-188Crossref PubMed Scopus (238) Google Scholar). Upon ligation with the A1 domain of vWF, the GP Ib-IX-V complex transmits inward a signal that leads to activation of integrin αIIbβ3 and eventual platelet activation and aggregation (3Andrews R.K. Shen Y. Gardiner E.E. Dong J.F. Lopez J.A. Berndt M.C. Thromb. Haemost. 1999; 82: 357-364Crossref PubMed Scopus (109) Google Scholar, 4Andrews R.K. Gardiner E.E. Shen Y. Whisstock J.C. Berndt M.C. Int. J. Biochem. Cell Biol. 2003; 35: 1170-1174Crossref PubMed Scopus (158) Google Scholar). Although the GP Ib-IX-V complex is widely considered to comprise GP Ibα, GPIbβ, GP IX, and GP V with a 2:2:2:1 stoichiometry (5Berndt M.C. Gregory C. Kabral A. Zola H. Fournier D. Castaldi P.A. Eur. J. Biochem. 1985; 151: 637-649Crossref PubMed Scopus (150) Google Scholar, 6Du X. Beutler L. Ruan C. Castaldi P.A. Berndt M.C. Blood. 1987; 69: 1524-1527Crossref PubMed Google Scholar, 7Modderman P.W. Admiraal L.G. Sonnenberg A. von dem Borne A.E. J. Biol. Chem. 1992; 267: 364-369Abstract Full Text PDF PubMed Google Scholar), it is not clear how these subunits assemble into a functional receptor complex in the membrane, partly because intersubunit interactions are largely unknown. Abnormally low expression of the GP Ib-IX-V complex in human platelets can result from mutations in either GP Ibα, GP Ibβ, or GP IX, but not GP V (8Lopez J.A. Andrews R.K. Afshar-Kharghan V. Berndt M.C. Blood. 1998; 91: 4397-4418Crossref PubMed Google Scholar). Such phenomena can be reproduced in transfected Chinese hamster ovary (CHO) cells; missing any of the three subunits leads to no or significantly lowered surface expression of the GP Ib-IX complex (9Lopez J.A. Leung B. Reynolds C.C. Li C.Q. Fox J.E.B. J. Biol. Chem. 1992; 267: 12851-12859Abstract Full Text PDF PubMed Google Scholar, 10Lopez J.A. Weisman S. Sanan D.A. Sih T. Chambers M. Li C.Q. J. Biol. Chem. 1994; 269: 23716-23721Abstract Full Text PDF PubMed Google Scholar). In contrast, GP V is not required for efficient expression of the GP Ib-IX complex, although there are mixed reports on whether it enhances the complex expression (11Li C.Q. Dong J.F. Lanza F. Sanan D.A. Sae-Tung G. Lopez J.A. J. Biol. Chem. 1995; 270: 16302-16307Abstract Full Text Full Text PDF PubMed Scopus (72) Google Scholar, 12Calverley D.C. Yagi M. Stray S.M. Roth G.J. Blood. 1995; 86: 1361-1367Crossref PubMed Google Scholar). Furthermore, it has been shown in transfected cells that the GP Ib-IX complex assembles in the endoplasmic reticulum before being transported as a single entity to the plasma membrane. Failure of proper complex assembly results in prompt degradation of GP Ibα in the lysosome and accumulation of nonnative GP IX inside the cell (13Lopez J.A. Li C.Q. Weisman S. Chambers M. Blood. 1995; 85: 1254-1258Crossref PubMed Google Scholar, 14Dong J.F. Gao S. Lopez J.A. J. Biol. Chem. 1998; 273: 31449-31454Abstract Full Text Full Text PDF PubMed Scopus (61) Google Scholar). Although the interdependence among the subunits in the GP Ib-IX complex is well documented, the underlying reasons are not clear. The requirement of all three subunits to efficient surface expression of the complex posits the importance of intersubunit interactions to the proper assembly and therefore stability of the receptor complex. Based on the effects of mutations in GP Ibβ on the expression level of GP IX, the N-terminal cysteine knot region in GP Ibβ was suggested to mediate the interaction with GP IX (15Kenny D. Morateck P.A. Montgomery R.R. Blood. 2002; 99: 4428-4433Crossref PubMed Scopus (17) Google Scholar). It helps to explain the dependence of GP IX expression on GP Ibβ. Why the expression of GP Ibα is dependent on GP Ibβ and/or IX nonetheless remains The transmembrane domains of GP Ibα and IX be to efficient surface expression of the GP Ib-IX complex. of either the or domain of GP Ibα not significantly complex expression in transfected cells C.Q. Dong J.F. Lopez J.A. Thromb. Haemost. 2002; PubMed Scopus Google Scholar, J.F. Li C.Q. Sae-Tung G. Afshar-Kharghan V. Lopez J.A. PubMed Scopus Google Scholar). the Ibα domain, but not the and can be with from the receptor expression level of the receptor complex T. S. J. Blood. 2002; PubMed Scopus Google Scholar). In a single-site mutation in the IX domain was to expression of the GP Ib-IX-V complex in a X. J. M. G. X. Ruan C. Thromb. Haemost. PubMed Scopus Google Scholar). It is not whether the Ibβ domain is as as its in GP Ibα and IX. mutations the Ibβ domain have been to surface expression of the receptor complex, although a mutation the and domains of GP Ibβ has S. T. T. T. H. J. 2002; PubMed Scopus Google Scholar). in a on the domains of the GP Ib-IX complex. found that the Ibβ domain with unrelated sequences produced the largest in with in GP Ibα and GP IX, on surface expression of the GP Ib-IX complex in transfected cells. have single-site mutations in the Ibβ domain that significantly decrease the complex expression by the stability of GP Ibα, suggesting that these mutations the interaction between GP Ibβ and In our interaction between in the Ibα domain and in the Ibβ domain, helps to explain the requirement of GP Ibβ for efficient expression of GP was used in on expression of the GP Ib-IX complex in cells (9Lopez J.A. Leung B. Reynolds C.C. Li C.Q. Fox J.E.B. J. Biol. Chem. 1992; 267: 12851-12859Abstract Full Text PDF PubMed Google Scholar, 10Lopez J.A. Weisman S. Sanan D.A. Sih T. Chambers M. Li C.Q. J. Biol. Chem. 1994; 269: 23716-23721Abstract Full Text PDF PubMed Google Scholar). The cell was from was by M. subunits of the GP Ib-IX complex, and were from or was from Replacement and of of the GP Ib-IX expression Ibα, Ibβ, or IX (9Lopez J.A. Leung B. Reynolds C.C. Li C.Q. Fox J.E.B. J. Biol. Chem. 1992; 267: 12851-12859Abstract Full Text PDF PubMed Google Scholar, 10Lopez J.A. Weisman S. Sanan D.A. Sih T. Chambers M. Li C.Q. J. Biol. Chem. 1994; 269: 23716-23721Abstract Full Text PDF PubMed Google were used in the domain in with or sequences on of the domain in the were by mutations the In the the Ibα a site was to a site of the with and its two were with the the site in the and the site in the Ibα and the site was of the with and its In a site was at with and its the site at was with and its the site was with and its to the of the Ibβ was in In site was with and its the site the site in the was with and its a site was with and its of the into cells produced the GP Ib-IX complex at a level that is from the not the domain, the the or was with and into the that been and of the mutations were in the by was with and into the of the sequences were by of of cells with GP Ibα, GPIbβ, and GP IX was as J.A. Weisman S. Sanan D.A. Sih T. Chambers M. Li C.Q. J. Biol. Chem. 1994; 269: 23716-23721Abstract Full Text PDF PubMed Google and to the cells were into of the cell and in with bovine serum to to The cells in well were with of serum and transfected with a of of of that been in with in serum for at or two were to be was to the of a The for before the the was by of with bovine The cells were for before being and for and transfected cells were and with phosphate-buffered bovine serum cells from were mixed with of cell for and at for from the cell was from the by at for at the in was the of was mixed with in a to a membrane, and with was by and the was either to or a the of the the of Ibα or Ibβ was with by the of the and the of the from cells. expression of GP Ibα and IX were by as Y. Berndt M.C. Lopez J.A. Blood. PubMed Scopus Google Scholar). the transfected cells were with and with in the the cells were with for at with and with for at a with to the cells were in a the the of the cell was with the of cells being and that of cells the effects on surface expression of the GP Ib-IX complex in transfected it is that in expression be to the of as on in the was the cells were for and expression of GP Ibα as well as GP IX were with two of the transfected cell for overall expression and for surface Furthermore, in a was by the of or Ibα, Ibβ, and IX in and at the to cells in of a for was from the the was to the a in from of transfected cells by were from the the of a single with the mutations in the GP Ib-IX complex. Although the is the in any it from to a of surface expression from cells transfected with and transfected with Ibα, Ibβ, and IX subunits were in The surface expression of complex were by the of the cell and with the of cells being and that of cells the surface expression level can be to the mutations in the It is to that although the with the surface expression is not a In a not that the of on the cell surface is of that of Replacing the of GP Ibα and GP Ibβ, but of GP IX, with in a domain is to the it can with domains in a complex. in the domain there is a that mediates interaction and to complex assembly and eventual surface the domain with as the or the and a in the J.A. B. J.A. 2001; PubMed Scopus Google Scholar). and have been used to the region in B. D. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar, C. H. Biol. PubMed Scopus Google Scholar, Biol. PubMed Scopus Google Scholar). the between the and at of not the interaction in the domain in the GP Ib-IX complex is for its efficient surface we the at a with the and sequences and effects on complex expression in transfected cells. in GP Ibα for the N-terminal of the domain were by either the or in GP Ibβ and in GP IX were The were transiently transfected into cells with the two In cells are by the transfected with the of the mutation Lack of the cells the cells transfected by the Ibα with the domain with Ibβ and IX The effects of mutations on complex expression in the cell were through of GP Ibα and IX from cell GP Ibα was with two that produced the In with the Ibα expression were in and cells. were in and cells. In contrast, no in Ibα expression was in and cells. GP IX was with a and the IX expression in transfected cells were with of GP The surface expression of GP Ibα and IX in cells mutations were by and with the transfected cells and were as and produced GP Ibα or GP IX on the cell surface at a level significantly with the that all three subunits are required for efficient surface expression of the GP Ib-IX complex (9Lopez J.A. Leung B. Reynolds C.C. Li C.Q. Fox J.E.B. J. Biol. Chem. 1992; 267: 12851-12859Abstract Full Text PDF PubMed Google Scholar, 10Lopez J.A. Weisman S. Sanan D.A. Sih T. Chambers M. Li C.Q. J. Biol. Chem. 1994; 269: 23716-23721Abstract Full Text PDF PubMed Google Scholar). It is that the surface expression level of GP Ibα or GP IX is not the in these partly transfected cells; cells significantly GP Ibα and cells GP IX cells. all of the and cells the surface expression of GP Ibα and IX, with of the of cells. The expression in and cells were cells but cells. In contrast, surface expression in cells was from the The expression in cells were significantly with the being of the surface expression of the Ibα and IX subunits was with overall expression in the cell. results that the domains of GP Ibα or GP Ibβ, but not that of GP IX, with unrelated to a decrease in expression of the GP Ib-IX complex, suggesting the importance of the Ibα and Ibβ domains in the complex Mutations of the between GP Ibα and GP between GP Ibα and Ibβ is to the domains. whether mutations of intersubunit cell were in a and for GP Ibα In the to GP the intersubunit or no GP was in and that of the intersubunit was either the Ibα or Ibβ domain was with unrelated It is to that the was in cells but was diminished in cells. suggested that the IX domain with the but not the with the in cells in the was largely of GP Ibα with in a complex with is with that of a Ibα was in cells GP Ibα T. J. Blood. Google Scholar). In our results that the Ibα and Ibβ domains are to of the between the two Replacing either domain with unrelated the interaction between the two in of the and of GP The role of the IX domain in of the a results were it was with unrelated Mutations in the Ibβ of GP Ibα and the the that decrease in the GP Ib-IX complex expression by is to the of the or of the of the we to mutations the domains that surface expression of GP Ib-IX complex. its largest effect by we on the Ibβ the of domain with the is the of all of the with be to the interaction with GP Ibα and efficient surface expression of the receptor complex. The of a domain that its with be on the for the we the in the Ibβ domain into of of the and was as of the on at a were to of the as to was transiently with Ibα and IX subunits into cells. The expression of subunits in cells were and as a of of the in cells. the three and in significantly lowered expression of GP Ibα in the cell The in in the expression level of GP The expression of GP Ibβ and IX in cells were but not with the Ibα expression Although and cells produced of GP Ibβ in the cell and of the expression level in a in expression of GP Ibα was and of the Ibα expression level in In the three cells in GP Ibα expression was the Ibβ expression to the was the Ibα the of GP Ibα and GP Ibβ in cells were and of in cells. that the Ibα expression was not by the expression of GP Ibβ. the decrease in Ibα expression was probably to the decrease in Ibα stability as a result of the interaction between GP Ibα and GP Ibβ. In to the in overall expression was between the surface expression of GP Ibα and IX in cells with the that the GP Ib-IX complex in the endoplasmic reticulum and is transported to the cell surface as a single Furthermore, the surface expression in the cells well with the overall expression of GP Ibα of GP the three cells with the overall expression of GP Ibα produced the Ib-IX complex on the cell results suggested that surface expression of the complex was by the stability of GP Ibα in the cell. the effects of of the single-site mutations in the and and from and from and and from effects on the overall expression of subunits were as in the cells Furthermore, between surface expression of GP Ibα and IX was for all of the single-site and the effects on surface expression of the Ib-IX complex well with the Ibα expression in the cell. effect on expression of GP Ibα, the mutations markedly the Ibα expression The expression level of GP Ibβ in to the was low that it expression of GP Ibα in the cell. the expression of GP Ibβ in the cells were that of GP in the expression level of GP Ibα in the with of the level the cells produced the level of GP Ib-IX complex on the cell with a being of the In we have single-site mutations in the Ibβ domain, of significantly expression of GP The mutation H139L, in produced the largest effect. results demonstrated the importance of the Ibβ domain to efficient surface expression of the GP Ib-IX complex. S503L and S503V in the Ibα the on Ibα by in the Ibβ and a of the in the C. J. Biol. PubMed Scopus Google Scholar, 1998; PubMed Scopus Google Scholar). The Ibβ domain two polar and either in the to to decrease in surface expression of the GP Ib-IX complex. cells produced GP Ibβ of the GP Ibα expression of GP Ibα was not to the of GP Ibβ. it is that is in interaction with GP Ibα, and the mutation interaction and the stability of GP Ibα and surface expression of the complex. polar with polar in the through Biol. 2003; PubMed Scopus Google Scholar, A. Biol. PubMed Scopus Google Scholar), of the Ibα and Ibβ domains in GP Ibα as a potential for and in the Ibα domain that of and the of and in the L. J. J. Biol. 2001; PubMed Scopus Google Scholar). interactions in the a polar with result in of of the polar to the and therefore the complex. polar are with the complex stability not be as the interaction between and we whether the mutation S503L in the Ibα domain can the effect of on the surface expression of the GP Ib-IX complex. the effect of S503L in Ibβ single-site cells as well and of the and cells that the S503L mutation a decrease in Ibα the produced of GP Ibα in the expression of the GP Ib-IX complex was lowered in cells and Furthermore, S503L a effect in cells a single-site mutation in the Ibβ domain, reducing the Ibα expression in the cell by of the level the Ibα in and of GP Ibβ was although the of not that in Ibα expression of the GP Ib-IX complex in these cells was by the S503L the of in of the of from in cells to in cells and In contrast, cells produced GP Ibα but GP Ibβ cells and expression of the GP Ib-IX complex in cells was that in cells and In the S503L mutation reversed the effect on complex expression by the the of and are in of we the effect of the mutation The of that of S503V reversed the effect on Ibα expression by the mutation but the surface expression of the Ib-IX complex in cells Ibβ mutations and to the effect of S503V on was these results a interaction between and have demonstrated in that the Ibβ domain is to efficient surface expression of the GP Ib-IX complex in transfected cells. domain or mutations in the Ibβ domain to a decrease in Ibα expression in the cell and surface expression of the complex. The decrease of Ibα expression was not to the lowered expression of GP Ibβ, the Ibβ expression in the in of the of that in are of GP Furthermore, the of decrease in Ibα expression in the cell not with that in Ibβ. The decrease of Ibα expression by the Ibβ mutations be to the of the interaction between the Ibα and Ibβ domains and therefore the decrease in the stability of GP Ibα in the cell. In our results to a specific interaction between in the Ibα domain and in the Ibβ domain, S503L and S503V reversed the expression-decreasing effect of and not the Ibβ among the subunits are to the stability and of the GP Ib-IX-V complex. The interactions between GP Ibα and Ibβ, between GP Ibβ and IX, and between GP Ibα and V have been J.A. Weisman S. Sanan D.A. Sih T. Chambers M. Li C.Q. J. Biol. Chem. 1994; 269: 23716-23721Abstract Full Text PDF PubMed Google Scholar, C.Q. Dong J.F. Lanza F. Sanan D.A. Sae-Tung G. Lopez J.A. J. Biol. Chem. 1995; 270: 16302-16307Abstract Full Text Full Text PDF PubMed Scopus (72) Google Scholar, D. Morateck P.A. J.C. Montgomery R.R. Blood. 1999; PubMed Google Scholar). The interaction between GP Ibα and IX remains J.A. Weisman S. Sanan D.A. Sih T. Chambers M. Li C.Q. J. Biol. Chem. 1994; 269: 23716-23721Abstract Full Text PDF PubMed Google Scholar, G. Blood. PubMed Google Scholar). of its interaction with GP Ibα and IX, GP Ibβ a role in the assembly of the receptor complex J.A. Weisman S. Sanan D.A. Sih T. Chambers M. Li C.Q. J. Biol. Chem. 1994; 269: 23716-23721Abstract Full Text PDF PubMed Google Scholar). GP Ibβ with GP IX through its N-terminal cysteine knot region (15Kenny D. Morateck P.A. Montgomery R.R. Blood. 2002; 99: 4428-4433Crossref PubMed Scopus (17) Google Scholar). In the or between GP Ibα and GP Ibβ have although intersubunit the two The in suggested a interaction between the Ibα and Ibβ domains. our of the the Ibα or Ibβ domain a and specific interaction between the two domains and and interaction is in of the between the X. S. J. A. and for the domain of GP Ibα, as is found in the plasma from the GP Ib-IX-V complex on the platelet surface S. A. PubMed Scopus Google Scholar), it is that with the domains of subunits in the complex, or at interaction is not to of from the platelet has been no on the interaction between the domains of GP Ibα and GP Ibβ. the interaction between the two domains be the that mediates of GP Ibα and GP Ibβ. Such GP Ibα in the endoplasmic its Although our results interaction between the polar in the Ibα and Ibβ the interaction is to be the between the two domains. Although either with a decrease in expression of the GP Ib-IX complex, the of decrease not by mutations in and cells. that S503L mutations of the receptor complex. Furthermore, the three of the Ibβ to be The of and suggested that be a of the to all of the single-site mutations in and can expression of GP Ibα to that these in the interaction with GP the the effect of the mutation that is not on and but a decrease in the expression of GP Ibα, is the Ibβ domain a of the importance of was not probed by the It is that of the in the interaction between the Ibα and Ibβ domains. the and of the interaction between the Ibα and Ibβ domains a that is Replacing the Ibβ domain in a effect on complex expression the Ibα counterpart, suggesting for the Ibβ domain in complex assembly and is that the Ibβ domain with that of the GP IX, or the IX domain can the interaction between GP Ibα and GP Ibβ. Although the IX domain with the not of the it with the of the and domains of GP IX the expression of the GP Ib-IX-V complex in human suggesting that the IX domain is not for efficient surface expression of the complex M. T. T. T. M. A. A. A. Thromb. Haemost. 1995; PubMed Scopus Google Scholar). In a single-site mutation in the IX domain has been from a to the complex surface expression X. J. M. G. X. Ruan C. Thromb. Haemost. PubMed Scopus Google Scholar). the intersubunit interactions in the domains not be to the between GP Ibα and GP Ibβ. to the of the GP Ib-IX-V complex. The interaction between the Ibα and Ibβ domains to functional of the GP Ib-IX-V complex. the domain of GP Ibβ can of GP cells to C. S. M. C. C. J. M. S. Lanza F. Thromb. Haemost. 2001; 86: PubMed Scopus Google Scholar). of in the Ibβ domain mediates its interaction with the and the of GP Ibα Li X. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar, X. Li Berndt M.C. X. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus (72) Google Scholar, C. M. S. D. Lanza F. Blood. 2003; PubMed Scopus Google Scholar). The region of the Ibβ domain has been in the and platelet activation and aggregation G. D.C. D. J. Thromb. Haemost. 2003; PubMed Scopus Google Scholar). Furthermore, mutations in the Ibα and that the interaction can the J.F. Li C.Q. Sae-Tung G. Afshar-Kharghan V. Lopez J.A. PubMed Scopus Google Scholar, Berndt M.C. X. Blood. PubMed Scopus Google Scholar, M. Gao S. B. Lopez J.A. Dong J.F. 2003; PubMed Scopus Google Scholar). It is that signal can from the Ibα and/or Ibβ domain and with the in the as well as the of the N-terminal domain of GP Ibα the plasma membrane. It is that the interaction between the Ibα and Ibβ domains role in a signal the membrane. on the a with was and F. J. Thromb. Haemost. was to have the transmembrane and domains of GP Ibβ to a the importance of the transmembrane and domains of GP Ibβ in GP expression and is with our in Berndt for the and for on cell and