Faculty Collaboration Database

A dinucleotide deletion results in defective membrane anchoring and circulating soluble glycoprotein Ib alpha in a novel form of Bernard-Soulier syndrome. Blood 1997 Oct 01;90(7):2626-33

Date

11/05/1997

Pubmed ID

9326229

DOI

10.1182/blood.v90.7.2626.2626_2626_2633

Scopus ID

2-s2.0-0030794862 (requires institutional sign-in at Scopus site)   34 Citations

Abstract

The platelet membrane glycoprotein (GP)Ib-V-IX complex is the receptor for von Willebrand factor and is composed of four membrane-spanning polypeptides: GPIb alpha, GPIb beta, GPIX, and GPV. A qualitative or quantitative deficiency in the GPIb-V-IX complex on the platelet membrane is the cause of the congenital platelet disorder Bernard-Soulier syndrome (BSS). We describe the molecular basis of a novel variant BSS in a patient in which GPIb alpha was absent from the platelet surface but present in a soluble form in the plasma. DNA sequence analysis showed a homozygous dinucleotide deletion in the codon for Tyr 508 (TAT) in GPIb alpha. This mutation (GPIb alpha deltaAT) causes a frame shift that alters the amino acid sequence of GPIb alpha within its transmembrane region. The hydrophobic nature of the predicted transmembrane region and the cytoplasmic tail at the COOH terminal are altered before reaching a new premature stop codon 38 amino acids short of the wild-type peptide. Although GPIb alpha deltaAT was not detectable on the platelet surface, immunoprecipitation of plasma with specific monoclonal antibodies (MoAbs) identified circulating GPIb alpha. Transient expression of recombinant GPIb alpha deltaAT in 293T cells also generated a soluble form of the protein. Moreover, when a plasmid encoding GPIb alpha deltaAT was transiently transfected into Chinese hamster ovary (CHO) cells stably expressing the GP beta-IX complex, it failed to be expressed on the cell surface. Thus, a dinucleotide deletion in the codon for Tyr 508 causes a frameshift that alters the amino acid sequence of GPIb alpha starting within its transmembrane region, changes the hydrophobicity of the normal transmembrane region, and truncates the cytoplasmic domain affecting binding to the cytoskeleton and cytoplasmic proteins. This mutation affects anchoring of the GPIb alpha polypeptide in platelets and causes the observed BSS phenotype with circulating soluble GPIb alpha.

Author List

Kenny D, Newman PJ, Morateck PA, Montgomery RR

Author

Robert R. Montgomery MD Adjunct Professor in the Pediatrics department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

Aged
Amino Acid Sequence
Animals
Bernard-Soulier Syndrome
Blood Platelets
CHO Cells
Cell Membrane
Codon
Cricetinae
Cricetulus
Cytoplasm
Cytoskeleton
DNA Mutational Analysis
Female
Humans
Male
Molecular Sequence Data
Platelet Glycoprotein GPIb-IX Complex
Polymerase Chain Reaction
Protein Binding
Protein Structure, Secondary
Recombinant Fusion Proteins
Sequence Deletion