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Mutations of conserved arginines in the membrane domain of erythroid band 3 lead to a decrease in membrane-associated
P Jarolim1, H L Rubin, V Brabec
1Department of Biomedical Research, St Elizabeth's Medical Center, Tufts University School of Medicine, Boston, MA 02135.
Insights
Mutations in the band 3 protein cause hereditary spherocytosis (HS). Specific arginine substitutions prevent band 3 protein incorporation into red blood cell membranes, leading to band 3 deficiency in HS patients.
Area of Science:
- Genetics
- Molecular Biology
- Hematology
Background:
- Hereditary spherocytosis (HS) is a genetic blood disorder.
- Band 3 protein is crucial for red blood cell membrane integrity.
- A subset of HS patients exhibits band 3 deficiency.
Purpose of the Study:
- To identify the molecular basis of band 3 deficiency in hereditary spherocytosis.
- To investigate the impact of specific band 3 mutations on protein localization.
Main Methods:
- Screening of band 3 cDNA for single-strand conformation polymorphism (SSCP).
- Analysis of mutation inheritance patterns in HS patients.
- Utilizing a band 3 polymorphism (band 3 Memphis) to track mutant protein incorporation.
Main Results:
- Identified four arginine substitutions (R760W, R760Q, R808C, R870W) in 29% of HS patients with band 3 deficiency.
- These mutations were coinherited with the HS phenotype.
- Demonstrated that the R760Q mutation prevents the mutant band 3 protein from being incorporated into the red blood cell membrane.
Conclusions:
- Arginine substitutions in band 3 protein disrupt its membrane insertion.
- This disruption leads to band 3 deficiency in hereditary spherocytosis.
- Mutant protein loss may occur during erythroid precursor differentiation.
Abstract:
To elucidate the molecular basis of band 3 deficiency in a recently defined subset of patients with autosomal dominant hereditary spherocytosis (HS), we screened band 3 cDNA for single-strand conformation polymorphism (SSCP). In 5 of 17 (29%) unrelated HS subjects with band 3 deficiency, we detected substitutions R760W, R760Q, R808C, and R870W that were all coinherited with the HS phenotype. The involved arginines are highly conserved throughout evolution. To examine whether or not the product of the mutant allele is inserted into the membrane, we studied one HS subject who was doubly heterozygous for the R760Q mutation and the K56E (band 3sMEMPHIS) polymorphism that results in altered electrophoretic mobility of the band 3 Memphis proteolytic fragments. We detected only the band 3MEMPHIS in the erythrocyte membrane indicating that the protein product of the mutant, R760Q, band 3 allele is absent from the red blood cell membrane. These findings suggest that the R760Q substitution, and probably the other arginine subsitutions, produce band 3 deficiency either by precluding incorporation of the mutant protein into the red blood cell membrane or by leading to loss of mutant protein from differentiating erythroid precursors.