Interactions between mutant and wild-type band 3 subunits in hereditary Southeast Asian ovalocytic red blood cell membranes.
Red cell membranes from individuals with Southeast Asian ovalocytosis (SAO) contain approximately equal proportions of wild-type band 3 and a mutant SAO band 3 which lacks residues 400-408. It is known that the Vmax for anion exchange in SAO cells is reduced by about 50%, that SAO band 3 does not transport anions when expressed alone in a cellular expression system, that SAO band 3 does not bind stilbenedisulfonates, and that about 50% of the band 3 exists as wild-type/SAO heterodimers. In this report, we show that the kinetics of H2DIDS (4,4'-diisothiocyanatodihydro-2,2'-stilbenedisulfonate) release from the wild-type band 3 in SAO membranes is biphasic. The two phases were present in about equal proportions, with rate constants differing by about 5-fold. In contrast; control cells showed monophasic, exponential kinetics with a rate constant comparable to that of the fast phase of SAO membranes. We assign the fast phase in SAO membranes to H2DIDS release from wild-type subunits within homodimers and the slow phase to H2DIDS release from the wild-type subunit within the heterodimer. No differences were observed in kinetic studies of H2DIDS binding. These results suggest that the mutant band 3 subunit alters the conformation of its neighboring wild-type subunit within the heterodimer, resulting in about a 4-fold higher H2DIDS affinity. Additional evidence suggesting that the interactions in the heterodimer may be confined to a region of the wild-type subunit containing the C-terminal subdomain is presented. The relationship of these subunit interactions to the observation of a reduced cellular anion transport function is discussed.
Salhany
J M
JM
Veterans Administration Medical Center, Omaha, Nebraska, USA.
Schopfer
L M
LM
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000097:blood; D000740:Anemia / Q000097:blood* / Q000235:genetics*; D001457:Anion Exchange Protein 1, Erythrocyte / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D001210:Asia, Southeastern; D004913:Erythrocytes, Abnormal; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D008433:Mathematics; D017354:Point Mutation; D011485:Protein Binding; D013997:Time Factors
D001457:Anion Exchange Protein 1, Erythrocyte; D046911:Macromolecular Substances; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid