Ion Pumps PDF
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ADVANCES IN MOLECULAR AND CELL BIOLOGY ION PUMPS Series Editor: E. EDWARD BITTAR Department of Physiology University of Wisconsin Madison, Wisconsin Cuest Editor: JENS PETER ANDERSEN Institute of Physiology University of Aarhus Aarhus, Denmark ~~~ VOLUME 23A 1998 @]A, PRESS INC. Greenwich, Connecticut London, England Copyright 0 7998 IAI PRESS INC. 55 Old Post Road No. 2 Greenwich, Connecticut 06836 JAl PRESS LTD. 38 Tavistock Street Covent Garden London WCZE 7PB England All rights reserved. No part of this publication may be reproduced, stored on a retrieval system, or transmitted in any way, or by any means, electronic, mechanical, photocopying, recording, filming or otherwise without prior permission in writing from the publisher. ISBN: 0- 7623-028 7-9 Manufactured in the United States of America LIST OF CONTRIBUTORS Robert Aggeler Institute of Molecular Biology University of Oregon Eugene, Oregon Krister Barnberg Wadsworth Veterans Administration Medical Center Los Angeles, California Denis Bayle Wadsworth Veterans Administration Medical Center Los Angeles, California Roderick A. Capaldi Institute of Molecular Biology University of Oregon Eugene, Oregon Leopoldo de Meis Departamento de Bioquimica MCdica Universidade Federal do Rio de Janeiro Rio de Janeiro, Brazil Peter Dimroth Mikrobiologisches lnstitut Eidgenossische Technische Hochschule Zurich, Switzerland Jan Eggerrnont Laboratorium voor Fysiologie Katholieke Universiteit Leuven Leuven, Belgium Sirnone Engelender Departamento de Bioquimica M6dica Universidade Federal do Rio de Janeiro Rio de Janeiro, Brazil IX LIST OF CONTRIBUTORS X Agnes Enyedi National Institute of Haematology, Blood Transfusion and Immunology Budapest, Hungary Michael Forgac Department of Cellular and Molecular Physiology Tufts University Boston, Massachusetts Kathi Ceering Institute of Pharmacology and Toxicology University of Lausanne Lausanne, Switzerland Ursula Cerike School of Biology and Biochemistry University of Bath Bath, England james E. Haber Rosenstiel Basic Medical Sciences Research Center and Department of Biology Brandeis University Waltham, Massachusetts Parjit Kaur Department of Biology Georgia State Univesity Atlanta, Georgia Daniel Khananshvili Department of Physiology and pharmacology Sackler School of Medicine Tel-Aviv University Tel-Aviv, Israel David B. Mclntosh MRC Biomembrane Research Unit and Department of Chemical Pathology University of Cape Town Medical School Cape Town, South Africa Luc Mertens Laboratorium voor Fysiologie Katholieke Universiteit Leuven Leuven, Belgium john T. Penniston Department of Biochemistry and Molecular Biology Mayo ClinidFoundation Rochester, Minnesota List of Contributors xi David S. Perlin Public Health Research Institute New York, New York Luc Raeymaekers Laboratorium voor Fysiologie Katholieke Universiteit Leuven Leuven, Belgium George Sachs Wadsworth Veterans Administration Medical Center Los Angeles, California jai Moo Shin Wadsworth Veterans Administration Medical Center Los Angeles, California Marc Solioz Department of Clinical Pharmacology University of Berne Berne, Switzerland Ludo Van Den Bosch Laboratorium voor Fysiologie Katholieke Universiteit Leuven Leuven, Belgium Hilde Verboomen Laboratorium voor Fysiologie Katholieke Universiteit Leuven Leuven, Belgium Herman Wolosker Departamento de Bioquimica M6dica Universidade Federal do Rio de Janeiro Rio de Janeiro, Brazil Frank Wuytack Laboratorium voor Fysiologie Katholieke Universiteit Leuven Leuven, Belgium PREFACE Both eukaryotic and prokaryotic cells depend strongly on the function of ion pumps present in their membranes. The term ion pump, synonymous with active ion- transport system, refers to a membrane-associated protein that translocates ions up- hill against an electrochemicalp otential gradient. Primary ion pumps utilize energy derived from chemical reactions or from the absorption of light, while secondary ion pumps derive the energy for uphill movement of one ionic species from the downhill movement of another species. In the present volume, various aspects of ion pump structure, mechanism, and regulation are treated using mostly the ion-transportingA TPases as examples. One chapter has been devoted to a secondary ion pump, the Na+-Ca2+ex changer, not only because of the vital role played by this transport system in regulation of cardiac contractility, but also because it exemplifies the interesting mechanistic and struc- tural similarities between primary and secondary pumps. The cation-transportingA TPases fall into two major categories. The P-type AT- Pases (treated in eight chapters) are characterized by the formation during the cata- lytic cycle of an aspartyl phosphorylated intermediate, and by their rather simple subunit composition (one catalytic a-chain, supplemented in Na+,K+a nd H+,K+ pumps with a P-chain that has a crucial role in expression of functional pumps at the cell surface). The FN-type ATF'ases (treated in three chapters) do not form arecog- nizable phosphoenzyme intermediate and are composed of multiple different subunits whose individual roles are now beginning to be understood. Similarly, some of the anion-transporting ATPases (treated in a single chapter) seem to be xiii xiv PREFACE composed of multiple subunits with separate roles in ATP hydrolysis and ion trans- location. Although there are too many structural and functional differences between the various ion transport ATPase families to warrant speculations about a common evolutionary origin of all families, they do seem to resemble each other in some fundamental aspects. Thus, irrespective of whether an ATP- driven pump consists of one or several subunits, it has a large hydrophilic “pump head” protruding from the membrane, which is responsible for the ATP hydrolysis/synthesis reactions. The vectorial transport process is carried out by a more slender membrane-buried part forming a channel-like structure. En- ergy coupling seems to occur by long-range communication between the membrane-buried and extramembranous domains/subunits, mediated by con- formational changes. A major challenge is to elucidate the exact nature of the coupling process and to define the ion-translocation pathway through the membrane-buried part of the protein. As discussed in some of the chapters in this book, the distinction between ion pumps and ion channels now appears less sharp than previously, since several transporters can exhibit both types of function. It appears reasonable to consider an ion pump as a channel equipped with locks and gate controls. The three-dimensional structure of the extramembranousc atalytic F, part of F- type ATPases has recently been determined, and this has helped to provide a firm basis for speculations on the energy-coupling mechanism. Similarly, although a high-resolutionc rystal structure is still a distant goal in the case of P-type ATPases, analysis of the amino acid sequences of these pumps, in conjunction with various site-directed approaches such as mutagenesis and affinity labeling, has paved the way for realistic modeling of the structure of the ATP binding domain and its cou- pling with the ion transport domain. The topological features of the membranous part of P-type ATPases have long been a matter of conjecture, but several pieces of evidence now support a 10- transmembrane segment structure in Caz+-,H +,K+-,a nd Na+,K+-ATPases.A core region constituted by six of these transmembrane segments seems to have been re- tained also during evolution of P-type ATPases involved in heavy-metal-ion trans- port. The determinants of the specific ion selectivities of the pumps are poorly under- stood, but some interesting clues have been provided in studies of hybrids between H+- and Na+-transporting F-type ATPases and by comparing heavy-metal- transporting P-type ATPases with other P-type ATPases. Many ion pumps are known to occur as multiple isoenzymes differing with re- spect to tissue distribution and functional and regulatory characteristics. Regula- tion occurs both at the level of gene expression and through changes in hnetic parameters that determine the molecular pump rates. In health as well as in disease, control is exerted by the concentrationso f ions to be pumped and by hormonal and developmental influences. Although the molecular details of the regulatory events Preface xv are now beginnning to be understood, as described in several of the chapters in this volume, there seems to be much more to learn. Jens Peter Andersen Guest Editor REACTION MECHANISM OF THE SARCOPLASMIC RETICULUM Ca2+-ATP ase Herman Wolosker. Simone Engelender. and Leopoldo de Meis I.The RelaxingFactor ............................................ 2 I1 . The Calcium Pump ............................................ 3 111 . Phosphoenzyme of High Energy ................................... 4 IV. The Use of Chemiosrnotic Energy and the Reversal of Transport ATPases .... 5 V . Phosphorylation by Pi in the Absence of a Ca2+G radient ................ 8 VI . ATP + Pi Exchange in the Absence of a Ca2+G radient ..................1 0 VII . Net Synthesis of ATP in the Absence of a Ca'+ Gradient .................1 1 VIII . The Catalytic Cycle ............................................ 12 IX. The Partial Reactions of the Cycle ................................. 13 A . Reaction1 ................................................ 13 B . Reactions2 and 3 ........................................... 14 C . Reactions4and5 ........................................... 14 D. Reactions 6, 7, and 8 ........................................ 16 Advances in Molecular and Cell Biology . Volume 23A. pages 1.31 . Copyright 8 1998 by JAI Press Inc . All right of reproduction in any form reserved ISBN: 0-7623-0287-9 1 2 HERMAN WOLOSKER, SIMONE ENGELENDER, and LEOPOLDO de MElS E. Ca2+/H+C ountertransport. .................................... 17 X. Uncoupling of the Ca2+P ump .................................... 17 XI. UnidirectionalC a2+E fflux ....................................... 19 XII. Ca2+-ATPasel soform Diversity. ................................... 23 XIII.Summa ry .................................................... 23 1. THE RELAXING FACTOR The discovery of the Ca2+-ATPasei s intimately associated with the under- standing of the mechanism of muscle relaxation. The first report .of the Ca2+-ATPasew as published by Kielley and Meyerhof (1948). Who found a Mg2+-dependentA TPase activity separate from actomyosin that was associ- ated with the microsomal fraction of skeletal muscle (1952). At that time, the function of this new ATPase was unknown. Marsh showed that an aqueous muscle extract was able to induce swelling of muscle homogenate in the pres- ence of ATP, suggesting a relaxation process of the contractile proteins. Ben- dall (1952) further showed that the “Marsh” factor was also able to relax glycerinated fibers. Shortly after, it was recognized that the fraction contain- ing the Kielley-Meyerhof enzyme was identical to the “Marsh” relaxing factor (Kumagai et al., 1955) and corresponded to fragments of sarcoplasmic reticu- lum (Portzehl, 1957; Ebashi, 1958; Nagai et al., 1960; Muscatello et al., 1962). After these discoveries, different approaches were employed to study the mechanism of action of the relaxing factor, but few of them focused on the role of Ca2+i on in the process of muscle contraction and relaxation. Bendall had shown that the relaxing activity of the factor was inactivated by the addi- tion of low concentrations of Ca2+( Bendall, 1953). Furthermore, EDTA, a di- valent cation chelating agent, mimicked the relaxing factor by inducing relaxation of glycerinated fibers (Bozler, 1954). Weber (1959) later showed that the contraction and ATPase activity of myofibrils required low concentra- tions of Ca2+A. ware of these findings and working at the laboratory of Fritz Lipmann, Setsuro Ebashi (1960) found a relationship between Ca2+b inding capacities of various chelating agents and the ability to promote relaxation of glycerinated fibers. He soon realized that the relaxing factor is able to promote muscle relaxation by removing Ca2+f rom the contractile system . Ebashi (1961) also showed that the relaxing factor was able to bind Ca2+i n the pres- ence of ATP (Ebashi, 1961). Since the amount of Ca2+a ssociated with the re- laxing factor was low and it was not possible to detect any Ca2+-dependent ATPase activity, Ebashi thought that the Ca2+i ons bind to the membrane of sarcoplasmic vesicles, rather than being accumulated in an active process in- side the vesicles (Ebashi, 1961, Ebashi and Lipmann, 1962). Excellent re- views of the discovery of relaxing factor can be found in Ebashi and Endo (1968) and Ebashi, (1985).
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