NDLI: Substrate-dependent reversal of anion transport site orientation in the human red blood cell anion-exchange protein, AE1

Content Provider	PubMed Central
Author	Knauf, Philip A. Law, Foon-yee Leung, Tze-wah Vivian Gehret, Austin U. Perez, Martha L.
Abstract	The tightly coupled, one-for-one exchange of anions mediated by the human red blood cell AE1 anion-exchange protein involves a ping-pong mechanism, in which AE1 alternates between a state with the anion-binding site facing inward toward the cytoplasm (Ei) and a state with the site facing outward toward the external medium (Eo). The conformational shift (Ei ↔ Eo) is only permitted when a suitable substrate such as Cl− or HCO \documentclass[10pt]{article}\usepackage{amsmath}\usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{pmc}\usepackage[Euler]{upgreek}\pagestyle{empty}\oddsidemargin -1.0in\begin{document}\begin{equation}_{3}^{-}\end{equation}\end{document} (B−) is bound. With no anions bound, or with Cl− bound, far more AE1 molecules are in the inward-facing than the outward-facing forms (Ei ≫ Eo, ECli ≫ EClo). We have constructed a model for CI−–B− exchange based on Cl−–Cl− and B−–B− exchange data, and have used it to predict the heteroexchange flux under extremely asymmetric conditions, with either all Cl− inside and all B− outside (Cli-Bo) or vice versa (Bi-Clo). The experimental values of the ratio of the exchange rate for Bi-Clo to that for Cli-Bo are only compatible with the model if the asymmetry of bicarbonate-loaded sites (AB = EBo/EBi) > 10, the opposite of the asymmetry for unloaded or Cl-loaded sites. Furthermore, the Eo form has a higher affinity for HCO \documentclass[10pt]{article}\usepackage{amsmath}\usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{pmc}\usepackage[Euler]{upgreek}\pagestyle{empty}\oddsidemargin -1.0in\begin{document}\begin{equation}_{3}^{-}\end{equation}\end{document} than for Cl−, whereas the Ei form has a higher affinity for Cl−. The fact that this “passive” system exhibits changes in substrate selectivity with site orientation (“sidedness”), a characteristic usually associated with energy-coupled “active” pumps, suggests that changes in affinity with changes in sidedness are a more general property of transport proteins than previously thought.
Related Links	http://dx.doi.org/10.1073/pnas.162402399
Starting Page	10861
File Format	PDF
ISSN	10916490
e-ISSN	10916490
Journal	Proceedings of the National Academy of Sciences of the United States of America
Issue Number	16
Volume Number	99
Language	English
Publisher	National Academy of Sciences
Publisher Date	2002-08-06
Access Restriction	Open
Rights Holder	National Academy of Sciences
Subject Keyword	Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Multidisciplinary

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