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Three novel β‐propeller mutations causing Glanzmann thrombasthenia result in production of normally stable pro‐α IIb , but variably impaired progression of pro‐α IIb β 3 from endoplasmic reticulum to Golgi
Author(s) -
NELSON E. J. R.,
LI J.,
MITCHELL W. B.,
CHANDY M.,
SRIVASTAVA A.,
COLLER B. S.
Publication year - 2005
Publication title -
journal of thrombosis and haemostasis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.947
H-Index - 178
eISSN - 1538-7836
pISSN - 1538-7933
DOI - 10.1111/j.1538-7836.2005.01593.x
Subject(s) - mutant , golgi apparatus , endoplasmic reticulum , microbiology and biotechnology , alpha (finance) , mutant protein , platelet , immunoprecipitation , thrombasthenia , biology , chemistry , biochemistry , gene , medicine , immunology , construct validity , nursing , patient satisfaction , platelet aggregation
Summary. Background: Glanzmann thrombasthenia (GT) is an autosomal recessive bleeding disorder characterized by lack of platelet aggregation in response to most physiological agonists and caused by either a lack or dysfunction of the platelet integrin α IIb β 3 (glycoprotein IIb/IIIa). Objectives: To determine the molecular basis of GT and characterize the mutations by in vitro expression studies. Patients: We studied three unrelated patients from southern India whose diagnosis was consistent with GT. Results: Immunoprecipitation of the cell lysates and immunoblotting showed no detectable mature α IIb in the G128S mutant, in contrast to 6% and 33% of the normal amount of mature α IIb in the S287L and G357S mutants, respectively. Pulse‐chase analysis demonstrated pro‐ α IIb in the mutants comparable with the normal pro‐ α IIb , but no conversion to mature α IIb in the G128S mutant, and only trace conversion to mature α IIb in the S287L and G357S mutants. The disappearance of pro‐ α IIb in the three mutants was similar to that in cells expressing normal α IIb β 3 or α IIb only. All three mutants demonstrated pro‐ α IIb β 3 complexes and co‐localized with an ER marker by immunofluorescence. The G128S mutant showed no co‐localization with a Golgi marker, and the other two mutants showed minimal and moderate co‐localization with the Golgi marker. Conclusions: These three β ‐propeller mutations do not affect the production of pro‐ α IIb , its ability to complex with β 3 , or its stability, but do cause variable defects in transport of pro‐ α IIb β 3 complexes from the endoplasmic reticulum to the Golgi.