The structural basis of calcium transport by the calcium pump

Olesen, Claus; Picard, Martin; Winther, A.M.L.; Nielsen, CH; Morth, J. Preben; Oxvig, Claus; Møller, Jørgen; Nissen, P.

doi:10.1107/s0108767308088077

Cited by 140 publications

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“…To propose an activation mechanism for KtrAB we need to define its 'gates' (that is, regions that undergo a conformational change and close/open the ion pathway)-ion transporters 25 and Version: Postprint (identical content as published paper) This is a self-archived document from i3S -Instituto de Investigação e Inovação em Saúde in the University of Porto Open Repository For Open Access to more of our publications, please visit http://repositorio-aberto.up.pt/ A01/00 channels 26 can have multiple gates. In KtrAB, the intramembrane loop has been proposed to be a gate 9,19 .…”

Section: Implications For Ktrab Activationmentioning

confidence: 99%

The structure of the KtrAB potassium transporter

Vieira-Pires

Szöllősi

Morais-Cabral

2013

Nature

106

163

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In bacteria, archaea, fungi and plants the Trk, Ktr and HKT ion transporters are key components of osmotic regulation, pH homeostasis and resistance to drought and high salinity. These ion transporters are functionally diverse: they can function as Na + or K + channels and possibly as cation/K + symporters. They are closely related to potassium channels both at the level of the membrane protein and at the level of the cytosolic regulatory domains. Here we describe the crystal structure of a Ktr K + transporter, the KtrAB complex from Bacillus subtilis. The structure shows the dimeric membrane protein KtrB assembled with a cytosolic octameric KtrA ring bound to ATP, an activating ligand. A comparison between the structure of KtrAB-ATP and the structures of the isolated fulllength KtrA protein with ATP or ADP reveals a ligand-dependent conformational change in the octameric ring, raising new ideas about the mechanism of activation in these transporters.The Trk/Ktr/HKT superfamily of ion transporters includes the Trk, Ktr and HKT transporter families 1 . These transporters are closely related to the superfamily of tetrameric cation channels 2-4 , which includes potassium, sodium and calcium channels. The membrane proteins in both superfamilies share the same architecture 2,5-9 : four subunits or repeats, each with the TM-P loop-TM (where TM indicates transmembrane helix) structural motif first seen in the KcsA potassium channel structure 10 , assemble to form an ion pore with a 'selectivity filter' along its central axis. In addition, the cytosolic regulatory proteins of the Trk and Ktr transporters and of the MthK 11,12 and large-conductance Ca 2+ -gated (BK) K + channels [13][14][15] are RCK (regulate conductance of K+) domains.Ktr ion transporters are crucial K + transport systems in some bacteria 16,17 , with a role in resistance to osmotic stress and high salinity by mediating the early uptake of K + (refs 16, 18). The Ktr ion transporters are composed of two essential components 3,16 : a membrane protein (KtrB or KtrD) and a cytosolic regulatory protein (KtrA or KtrC). Studies with cells show that Ktr proteins 8,19 transport K + but are also permeable to Na + , and that K + transport is ATP 20 and Na + dependent 5,8,18 . Furthermore, it has been shown that truncated KtrA forms octameric rings 21,22 and that KtrB assembles as homodimers 6,21 . The structures described here clarify the molecular basis of some of these properties as well as the structural relationship between these transporters and ion channels.

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Section: Implications For Ktrab Activationmentioning

confidence: 99%

The structure of the KtrAB potassium transporter

Vieira-Pires

Szöllősi

Morais-Cabral

2013

Nature

106

163

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“…Based on homology modeling using the Na + /K + -ATPase as a template, these residues were mapped to a region of the SERCA Ca 2+ -ATPase that forms a binding pocket for a PE molecule in the E2 conformation [127,128]. This PE molecule has been proposed to assist Ca 2+ entry into a deep, funnel-shaped and negatively charged path that leads to the Ca 2+ coordination sites located halfway through the membrane bilayer [128,129]. The binding pocket is not accessible in the E1 conformation, implying that the PE molecule has to dynamically enter and exit the pocket as the SERCA Ca 2+ -ATPase proceeds through the catalytic cycle.…”

Section: Putative Phospholipid Flipping Mechanism Of P4-atpasesmentioning

confidence: 99%

Structure and mechanism of ATP-dependent phospholipid transporters

López‐Marqués

Poulsen

Bailly

et al. 2015

Biochimica et Biophysica Acta (BBA) - General Subjects

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Background: ATP-binding cassette (ABC) transporters and P4-ATPases are two large and seemingly unrelated families of primary active pumps involved in moving phospholipids from one leaflet of a biological membrane to the other. Scope of review: This review aims to identify common mechanistic features in the way phospholipid flipping is carried out by two evolutionarily unrelated families of transporters. Major conclusions: Both protein families hydrolyze ATP, although they employ different mechanisms to use it, and have a comparable size with twelve transmembrane segments in the functional unit. Further, despite differences in overall architecture, both appear to operate by an alternating access mechanism and during transport they might allow access of phospholipids to the internal part of the transmembrane domain. The latter feature is obvious for ABC transporters, but phospholipids and other hydrophobic molecules have also been found embedded in P-type ATPase crystal structures. Taken together, in two diverse groups of pumps, nature appears to have evolved quite similar ways of flipping phospholipids. General significance: Our understanding of the structural basis for phospholipid flipping is still limited but it seems plausible that a general mechanism for phospholipid flipping exists in nature. This article is part of a Special Issue entitled Structural biochemistry and biophysics of membrane proteins.

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“…This latter designation must define two conformations; indeed, both have been crystallized in the case of the Ca-ATPase [15,16,27]. One is the form that releases the cytoplasmically bound ions into the lumen in reversible fashion; this form readily rebinds the ions and converts back to the E1P form.…”

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confidence: 99%

Outside of the box: recent news about phospholipid translocation by P4 ATPases

Stone

Williamson

2012

J Chem Biol

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The P4 subfamily of P-type ATPases includes phospholipid transporters. Moving such bulky amphipathic substrate molecules across the membrane poses unique mechanistic problems. Recently, three papers from three different laboratories have offered insights into some of these problems. One effect of these experiments will be to ignite a healthy debate about the path through the enzyme taken by the substrate. A second effect is to suggest a counterintuitive model for the critical substrate-binding site. By putting concrete hypotheses into play, these papers finally provide a foundation for investigations of mechanism for these proteins.Keywords P4 ATPase . Phospholipid transport . ATPase reaction cycleFraming the problem P-type ATPases are ATP-dependent ion transporters that derive their name from an aspartate that becomes transiently phosphorylated during the reaction cycle [17]. The structures of several members of the family have been determined at atomic resolution in the last decade, and they all have a large tripartite cytoplasmic domain and a small extracellular domain connected by six to ten transmembrane helices. The P4 subfamily of P-type ATPases was first defined in 1996, when the gene encoding an aminophospholipid translocase, ATP8A1, from bovine chromaffin granules [26] was found to be a relative of the previously identified yeast P-type ATPase, Drs2p [23]. P4 type ATPases are found in all eukaryotic organisms but not in prokaryotes. In vertebrates, there are 14 genes that encode P4 ATPases [9] while in yeast there are five; Drs2, Dnf1, Dnf2, Dnf3, and Neo1 [19]. Unlike the other subfamilies of P-type ATPases, which all transport simple ions, the only known substrates of the P4 ATPases are phospholipids.The transport mechanism of the P-type ATPases depends on sequential partial reactions of ATP hydrolysis-phosphorylation and dephosphorylation of the critical aspartic acid residue in the cytoplasmic P domain-and linked sequential conformational changes; coordination between chemical and conformational steps drives substrate across the membrane against a concentration gradient. The conformational changes link a binding pocket for the transported ion to either the cytoplasm (the E1 conformation) or the extracytoplasmic, or lumenal space (the E2 conformation). In the classic Post-Albers model [1,22], binding of ions in the E1 conformation enables phosphorylation to the E1P form; this form is conformationally unstable, and converts to the E2P conformation. Loss of ions into the luminal space from that conformation is the key to dephosphorylation to the E2 form. The latter is also conformationally unstable, and the enzyme thus converts back into the E1 conformation [1,22].There is a subtlety about this sequence of events which should be mentioned here, particularly as it applies to the E2P conformation. This latter designation must define two conformations; indeed, both have been crystallized in the case of the Ca-ATPase [15,16,27]. One is the form that releases the cytoplasmically bound ions into th...

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The structural basis of calcium transport by the calcium pump

Abstract: After the transition, the crystal totally recovers its crystalline state and diffraction power. The symmetry is reduced from space-group I222 to its subgroup P21212 but the effects of this symmetry breaking on the structure are subtle.

Cited by 140 publications

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The structure of the KtrAB potassium transporter

The structure of the KtrAB potassium transporter

Structure and mechanism of ATP-dependent phospholipid transporters

Outside of the box: recent news about phospholipid translocation by P4 ATPases

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