Interaction of glyceraldehyde-3-phosphate dehydrogenase with the cytoplasmic pole of band 3 from bovine erythrocyte membrane: the mode of association and identification of the binding site of band 3 polypeptide.

Four fragments derived from the cytoplasmic pole of bovine band 3 were isolated, and their ability to bind glyceraldehyde-3-phosphate dehydrogenase from bovine erythrocyte and their amino-terminal primary structure were examined. It was suggested that the 50-kDa fragment, an entire cytoplasmic pole of band 3, contained the blocked amino-terminal end of band 3. Three other fragments, 45-, 39-, and 38-kDa fragments, were produced by cleavage at distances of molecular weight 5000, 11,000, and 12,000 respectively, from the amino-terminus of the 50-kDa fragment. Among these, the 50- and 45-kDa fragments complexed with the enzyme to inhibit its catalytic activity under conditions of low ionic strength, in a fashion similar to that in humans. Affinity for the enzyme was not significantly affected by disruption of the higher order structure of the fragments. The enzyme was found to be inactivated by association with synthetic polyanions, accompanied by conformational alteration. This supports participation of electrostatic interactions as the holding force between the enzyme and band 3, as suggested by I-H. Tsai et al. [1982) J. Biol. Chem. 257, 1438-1442). The 45-kDa fragment was just as potent an inhibitor of the enzyme as the parent fragment, and its amino-terminal region displayed a polyanionic character. These results allow us to map the enzyme binding site of bovine band 3 to a distance of molecular weight approximately 5000 from the amino-terminal end of band 3. Furthermore, comparison of sequence data from different species showed that the species-specific region of band 3 polypeptide centers around the amino-terminal portion.