title: Mutation in the leucine-rich repeat C-flanking region of platelet glycoprotein Ib beta impairs assembly of von Willebrand factor receptor.
abstract: We describe a syndrome of thrombocytopenia, bleeding episodes, congenital heart disease and facial dysmorphism in a newborn infant, and trace the cause to mutations on chromosome 22 that involve the gene for platelet glycoprotein Ib beta (GPIb beta, Human Genome Organisation gene symbol GPIBB), a critical component of the von Willebrand factor (vWF) receptor. Fluorescence in situ hybridization in transformed lymphoblasts revealed hemizygous microdeletion of 22q11.2 containing the GP1BB locus. DNA sequencing revealed a C to T transition in the patient's remaining GP1BB allele, predicting a novel proline to serine substitution (Pro96Ser) in the carboxyterminal flanking domain of a leucine-rich repeat. We characterized the mutant GP1BB allele by expression in a cell line (CHO alpha IX) that stably expresses two other components of the vWF receptor, GPIb alpha and GPIX. Flow cytometry and confocal imaging of transfected CHO alpha IX cells demonstrated that P96S GPIb beta abrogates surface assembly of the complex, consistent with platelet flow cytometry studies in the patient. Based on sequence homology to the known crystal structures of two other leucine-rich repeat proteins, the human Nogo receptor and GPIb alpha, we propose a new structural model of GPIb beta. The model refutes earlier assumptions about cysteine-cysteine interactions in the amino-terminal region of GPIb beta, and predicts a hydrophobic patch the burial of which may contribute to proper conformation of the fully assembled vWF receptor complex.
authors.affiliation: Unit on Pediatric Genetics, Laboratory of Clinical Genomics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Jingrong
authors.initials: J
authors.lastname: Tang
authors.forename: Sara
authors.initials: S
authors.lastname: Stern-Nezer
authors.forename: Po-Ching
authors.initials: PC
authors.lastname: Liu
authors.forename: Ludmila
authors.initials: L
authors.lastname: Matyakhina
authors.forename: Michael
authors.initials: M
authors.lastname: Riordan
authors.forename: Naomi L C
authors.initials: NL
authors.lastname: Luban
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Steinbach
authors.forename: Stephen G
authors.initials: SG
authors.lastname: Kaler
mesh_terms: D000015:Abnormalities, Multiple / Q000235:genetics; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D002872:Chromosome Deletion; D002892:Chromosomes, Human, Pair 22 / Q000235:genetics; D019465:Craniofacial Abnormalities / Q000235:genetics; D006224:Cricetinae; D018076:DNA, Complementary / Q000235:genetics; D006330:Heart Defects, Congenital / Q000235:genetics; D006470:Hemorrhage / Q000097:blood / Q000235:genetics; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D007231:Infant, Newborn; D008297:Male; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D010980:Platelet Membrane Glycoproteins / Q000737:chemistry / Q000378:metabolism*; D017354:Point Mutation; D011487:Protein Conformation; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013577:Syndrome; D013921:Thrombocytopenia / Q000097:blood / Q000235:genetics*; D014162:Transfection
chemical_list: D018076:DNA, Complementary; D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface; C028254:von Willebrand factor receptor