title: The dimerization interface of the glycoprotein Ibβ transmembrane domain corresponds to polar residues within a leucine zipper motif.
abstract: Experiments with the transmembrane (TM) domains of the glycoprotein (GP) Ib-IX complex have indicated that the associations between the TM domains of these subunits play an important role in the proper assembly of the complex. As a first step toward understanding these associations, we previously found that the Ibβ TM domain dimerized strongly in Escherichia coli cell membranes and led to Ibβ TM-CYTO (cytoplasmic domain) dimerization in the SDS-PAGE assay, while neither Ibα nor IX TM-CYTO was able to dimerize. In this study, we used the TOXCAT assay to probe the Ibβ TM domain dimerization interface by Ala- and Leu-scanning mutagenesis. Our results show that this interface is based on a leucine zipper-like heptad repeat pattern of amino acids. Mutating either one of polar residues Gln129 or His139 to Leu or Ala disrupted Ibβ TM dimerization dramatically, indicating that polar residues might form part of the leucine zipper-based dimerization interface. Furthermore, these specific mutational effects in the TOXCAT assay were confirmed in the thiol-disulfide exchange and SDS-PAGE assays. The computational modeling studies further revealed that the most likely leucine zipper interface involves hydrogen bonding of Gln129 and electrostatic interaction of the His139 side chain. Correlation of computer modeling results with experimental mutagenesis studies on the Ibβ TM domain may provide insights for understanding the role of the association of TM domains on the assembly of GP Ib-IX complex.
authors.affiliation: Beijing Key Laboratory of Bioprocess, College of Life Science and Technology, Beijing University of Chemical Technology, Beijing 100029, People's Republic of China.
authors.forename: Peng
authors.initials: P
authors.lastname: Wei
authors.forename: Xin
authors.initials: X
authors.lastname: Liu
authors.forename: Miao-Hui
authors.initials: MH
authors.lastname: Hu
authors.forename: Li-Min
authors.initials: LM
authors.lastname: Zuo
authors.forename: Ming
authors.initials: M
authors.lastname: Kai
authors.forename: Rui
authors.initials: R
authors.lastname: Wang
authors.forename: Shi-Zhong
authors.initials: SZ
authors.lastname: Luo
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D002462:Cell Membrane / Q000737:chemistry* / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D006860:Hydrogen Bonding; D016350:Leucine Zippers; D008958:Models, Molecular; D009154:Mutation; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000737:chemistry* / Q000378:metabolism; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D020539:Sequence Analysis, Protein; D055672:Static Electricity
chemical_list: D019038:Platelet Glycoprotein GPIb-IX Complex