Further studies on Zn2+ -mediated domain-domain communication in human erythrocyte band 3

Human erythrocyte band 3 is purified and reconstituted into vesicles, forming right-side-out proteoliposomes. Zn2+ entrapped inside the proteoliposomes inhibits the anion transport activity of band 3, and removal of the cytoplasmic domain of band 3 is able to diminish Zn2+ inhibition. Thus, the inhibition of activity of band 3 results from the Zn2+ induced conformational change of the cytoplasmic domain, which in turn is transmitted to the membrane domain. The results of intrinsic fluorescence and its quenching by HB and the 35Cl NMR study indicate that the cytoplasmic domain is essential for the conformational change induced by Zn2+. SH-blocking reagents, CH(3)I and GSSG, are used to modify the cytoplasmic domain, where they specifically bind to Cys201 and Cys317. It is observed that the Zn2+ induced inhibition of anion transport activity is blocked. This demonstrates that Cys201 and Cys317 are required in Zn2+ -mediated domain-domain communication.