Identification of band 3 homologues in nonerythroid cell types
Abstract
Band 3, the predominant protein of the erythrocyte membrane, performs both anion transport and peripheral protein binding functions that are essential to the normal operations of the erythrocyte. Because the above functions are thought to be necessary to other cells also, antibodies to erythrocyte band 3 were developed and used to screen several non-erythroid cells for band 3 homologues. The antibodies were characterized and found to be monospecific to band 3 in Western blots of erythrocyte membranes with a detection limit of 25 ng. A band 3 homologue was identified in the rat kidney using antibodies to erythrocyte band 3. The band 3 homologue present in the kidney is thought to play an important role in the regulation of urine acidification. An immunologically related isoform of erythrocyte band 3 was also found in cells of the superficial cortex of the human lens. This is the first non-erythroid cell to demonstrate the simultaneous presence of all the major components that make up the erythrocyte membrane cytoskeleton. Antibodies to erythrocyte band 3 were also found to cross-react with several polypeptides in cultured fibroblast obtained from normal human embryonic lung cells. In several of the non-erythroid cells, the presence of the erythrocyte cytoskeletal components, ankyrin and band 4.1, were also detected by similar immunological techniques. Recently a cDNA clone encoding a non-erythroid band 3 polypeptide was reported demonstrating that cell specific isoforms of band 3 do exist. Since the report described the amino acid sequence of the non-erythroid band 3, regions of the protein not homologous to erythrocyte band 3 were identified and targeted for antibody production using synthetic peptides as antigens. The specificities of these non-erythroid antibodies are currently under investigation and in initial experiments the antibodies were found to cross-react with several polypeptides in K562 cells. In conclusion, erythroid as well as non-erythroid band 3 homologues have been identified in various cell types and the presence of these immunoreactive homologues suggest that similarities may exist between the erythrocyte membrane and the membrane of other cells.
Degree
Ph.D.
Advisors
Low, Purdue University.
Subject Area
Biochemistry|Immunology
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