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Increased membrane protein phosphorylation and anion transport activity in chorea-acanthocytosis
O Olivieri1, L De Franceschi, L Bordin
1Istituto di Patologia Medica, University of Verona, Italy.
Insights
Altered protein phosphorylation in red blood cells may explain shape changes and anion transport issues in chorea-acanthocytosis, a neurodegenerative disorder.
Area of Science:
- Neurobiology
- Hematology
- Molecular Genetics
Background:
- Chorea-acanthocytosis is a neurodegenerative disorder.
- Erythrocyte membrane protein band 3 dysfunction is implicated.
- Investigated erythrocyte parameters in a patient.
Observation:
- Examined membrane composition, sulphate influx, and protein phosphorylation.
- Assessed kinase activities and screened the EPB3 gene for mutations.
Findings:
- Increased sulphate influx, Ser/Thr phosphorylation, and casein-kinase activity observed.
- Enhanced Tyr-phosphorylation of band 3 and poly(Glu, Tyr) kinase activity noted.
- Normal band 3 concentration, fatty acid composition, and EPB3 gene sequence.
Implications:
- Abnormal phosphorylation of band 2 and band 3 proteins may cause erythrocyte shape changes.
- Altered phosphorylation could increase anion transport in chorea-acanthocytosis.
- Suggests a potential mechanism for erythrocyte defects in this disorder.
Background And Objective:
Chorea-acanthocytosis is a disorder characterized by neuronal degeneration and the presence of acanthocytic erythrocytes on blood smear. The abnormal function and structure of the membrane protein band 3 are considered to be of pathogenetic relevance in determining the erythrocyte defect.
Methods:
In a clinically evident case of chorea-acanthocytosis, the following parameters were investigated: membrane cholesterol and fatty acid composition, sulphate influx (as a measure of the anion transport activity), membrane protein phosphorylation, membrane casein and tyrosin-kinase activities; moreover, the promoter and all exons of the EPB3 gene were screened for possible mutations by single strand conformational polymorphism (SSCP) study.
Results:
The sulphate influx, the Ser/Thr phosphorylation level, and the membrane casein-kinase activity were increased in chorea-acanthocytosis compared with normal controls. In the intact vanadate-treated 32P-labelled erythrocytes, Tyr-phosphorylation of the cytoplasmic domain of band 3, as well as the poly(Glu, Tyr) kinase activity in the membranes, were enhanced in the patient's sample. Apparent molecular weight and concentration of band 3 on SDS/PAGE analysis, membrane fatty acid composition and cholesterol/phospholipid molar ratio were normal and the SSCP study of EPB3 exons did not show any abnormal polymorphisms.
Interpretations And Conclusions:
An abnormal degree of phosphorylation of membrane proteins, in particular of band 2 (beta-subunit) and band 3, may contribute in determining both change of cell shape and increased anion transport in chorea-acanthocytosis.