MOLECULAR-BASIS OF SPECTRIN DEFICIENCY IN BETA-SPECTRIN DURHAM - A DELETION WITHIN BETA-SPECTRIN ADJACENT TO THE ANKYRIN-BINDING SITE PRECLUDES SPECTRIN ATTACHMENT TO THE MEMBRANE IN HEREDITARY SPHEROCYTOSIS

Citation
H. Hassoun et al., MOLECULAR-BASIS OF SPECTRIN DEFICIENCY IN BETA-SPECTRIN DURHAM - A DELETION WITHIN BETA-SPECTRIN ADJACENT TO THE ANKYRIN-BINDING SITE PRECLUDES SPECTRIN ATTACHMENT TO THE MEMBRANE IN HEREDITARY SPHEROCYTOSIS, The Journal of clinical investigation, 96(6), 1995, pp. 2623-2629
Citations number
48
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Medicine, Research & Experimental
ISSN journal
0021-9738
Volume
96
Issue
6
Year of publication
1995
Pages
2623 - 2629
Database
ISI
SICI code
0021-9738(1995)96:6<2623:MOSDIB>2.0.ZU;2-A
Abstract
We describe a spectrin variant characterized by a truncated beta chain and associated with hereditary spherocytosis. The clinical phenotype consists of a moderate hemolytic anemia with striking spherocytosis an d mild spiculation of the red cells. We describe the biochemical chara cteristics of this truncated protein which constitutes only 10% of the total beta spectrin present on the membrane, resulting in spectrin de ficiency, Analysis of reticulocyte cDNA revealed the deletion of exons 22 and 23, We show, using Southern blot analysis, that this truncatio n results from a 4,6-kb genomic deletion. To elucidate the basis for t he decreased amount of the truncated protein on the membrane and the o verall spectrin deficiency, we show that (a) the mutated gene is effic iently transcribed and its mRNA abundant in reticulocytes, (b) the mut ant protein is normally synthesized in erythroid progenitor cells, (c) the stability of the mutant protein in the cytoplasm of erythroblasts parallels that of the normal beta spectrin, and (d) the abnormal prot ein is inefficiently incorporated into the membrane of erythroblasts, We conclude that the truncation within the beta spectrin leads to inef ficient incorporation of the mutant protein into the skeleton despite its normal synthesis and stability, We postulate that this misincorpor ation results from conformational changes of the beta spectrin subunit affecting the binding of the abnormal heterodimer to ankyrin, and we provide evidence based on binding assays of recombinant synthetic pept ides to inside-out-vesicles to support this model.