Asymmetry and Mechanisms of Anion Transport and Inhibition of the Human Anion Exchange Protein, AE1

Tuesday, February 9, 1999 - 10:45am - 11:30am
Keller 3-180
Philip Knauf (University of Rochester Medical Center)
The anion exchange protein AE1 is expressed in human red blood cells and, in a truncated form, in the basolateral membrane of Type A intercalated cells of the kidney. This protein catalyzes a one-for-one exchange of anions, such as chloride and bicarbonate, by means of a ping- pong mechanism, in which the protein alternates between a form, Ei, with the anion transport site facing inward toward the cytoplasm, and a form, Eo, with the transport site facing toward the external medium. Evidence from both chloride and bicarbonate transport kinetics, at 0C and 38C, indicates that the protein is intrinsically asymmetric, with about 10 times more molecules in the Ei form than in the Eo form, even with equal anion concentrations at both sides of the membrane. This asymmetry has important effects on the apparent kinetic constants for the transport system, and alterations in the fraction of AE1 in each conformation strongly affect the binding of certain inhibitors, such as disulfonic stilbenes and oxonols. Both nuclear magnetic resonance (NMR) and fluorescence resonance energy transfer (FRET) provide important clues as to the relative locations of transport and inhibitor sites in the protein, and their location relative to the lipid bilayer. Comparative aspects of the function of AE1 relative to other members of the anion exchange family, such as AE2, will also be discussed. (Supported by NIH (NIDDK) Grant DK27495.)