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Clarke RJ. Electrostatic switch mechanisms of membrane protein trafficking and regulation. Biophys Rev 2023; 15:1967-1985. [PMID: 38192346 PMCID: PMC10771482 DOI: 10.1007/s12551-023-01166-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2023] [Accepted: 11/17/2023] [Indexed: 01/10/2024] Open
Abstract
Lipid-protein interactions are normally classified as either specific or general. Specific interactions refer to lipid binding to specific binding sites within a membrane protein, thereby modulating the protein's thermal stability or kinetics. General interactions refer to indirect effects whereby lipids affect membrane proteins by modulating the membrane's physical properties, e.g., its fluidity, thickness, or dipole potential. It is not widely recognized that there is a third distinct type of lipid-protein interaction. Intrinsically disordered N- or C-termini of membrane proteins can interact directly but nonspecifically with the surrounding membrane. Many peripheral membrane proteins are held to the cytoplasmic surface of the plasma membrane via a cooperative combination of two forces: hydrophobic anchoring and electrostatic attraction. An acyl chain, e.g., myristoyl, added post-translationally to one of the protein's termini inserts itself into the lipid matrix and helps hold peripheral membrane proteins onto the membrane. Electrostatic attraction occurs between positively charged basic amino acid residues (lysine and arginine) on one of the protein's terminal tails and negatively charged phospholipid head groups, such as phosphatidylserine. Phosphorylation of either serine or tyrosine residues on the terminal tails via regulatory protein kinases allows for an electrostatic switch mechanism to control trafficking of the protein. Kinase action reduces the positive charge on the protein's tail, weakening the electrostatic attraction and releasing the protein from the membrane. A similar mechanism regulates many integral membrane proteins, but here only electrostatic interactions are involved, and the electrostatic switch modulates protein activity by altering the stabilities of different protein conformational states.
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Affiliation(s)
- Ronald J. Clarke
- School of Chemistry, University of Sydney, Sydney, NSW 2006 Australia
- The University of Sydney Nano Institute, Sydney, NSW 2006 Australia
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Hossain KR, Clayton D, Goodchild SC, Rodger A, Payne RJ, Cornelius F, Clarke RJ. Order-disorder transitions of cytoplasmic N-termini in the mechanisms of P-type ATPases. Faraday Discuss 2021; 232:172-187. [PMID: 34549220 DOI: 10.1039/d0fd00040j] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Membrane protein structure and function are modulated via interactions with their lipid environment. This is particularly true for integral membrane pumps, the P-type ATPases. These ATPases play vital roles in cell physiology, where they are associated with the transport of cations and lipids, thereby generating and maintaining crucial (electro-)chemical potential gradients across the membrane. Several pumps (Na+, K+-ATPase, H+, K+-ATPase and the plasma membrane Ca2+-ATPase) which are located in the asymmetric animal plasma membrane have been found to possess polybasic (lysine-rich) domains on their cytoplasmic surfaces, which are thought to act as phosphatidylserine (PS) binding domains. In contrast, the sarcoplasmic reticulum Ca2+-ATPase, located within an intracellular organelle membrane, does not possess such a domain. Here we focus on the lysine-rich N-termini of the plasma-membrane-bound Na+, K+- and H+, K+-ATPases. Synthetic peptides corresponding to the N-termini of these proteins were found, via quartz crystal microbalance and circular dichroism measurements, to interact via an electrostatic interaction with PS-containing membranes, thereby undergoing an increase in helical or other secondary structure content. As well as influencing ion pumping activity, it is proposed that this interaction could provide a mechanism for sensing the lipid asymmetry of the plasma membrane, which changes drastically when a cell undergoes apoptosis, i.e. programmed cell death. Thus, polybasic regions of plasma membrane-bound ion pumps could potentially perform the function of a "death sensor", signalling to a cell to reduce pumping activity and save energy.
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Affiliation(s)
| | - Daniel Clayton
- School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia.
| | - Sophia C Goodchild
- Department of Molecular Sciences, Macquarie University, Sydney, NSW 2109, Australia
| | - Alison Rodger
- Department of Molecular Sciences, Macquarie University, Sydney, NSW 2109, Australia
| | - Richard J Payne
- School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia.
| | - Flemming Cornelius
- Department of Biomedicine, University of Aarhus, DK-8000 Aarhus C, Denmark
| | - Ronald J Clarke
- School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia. .,The University of Sydney Nano Institute, Sydney, NSW 2006, Australia
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Clarke R, Hossain K, Cao K. Physiological roles of transverse lipid asymmetry of animal membranes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2020; 1862:183382. [DOI: 10.1016/j.bbamem.2020.183382] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2020] [Revised: 06/01/2020] [Accepted: 06/02/2020] [Indexed: 02/07/2023]
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Hossain KR, Li X, Zhang T, Paula S, Cornelius F, Clarke RJ. Polarity of the ATP binding site of the Na +,K +-ATPase, gastric H +,K +-ATPase and sarcoplasmic reticulum Ca 2+-ATPase. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2019; 1862:183138. [PMID: 31790695 DOI: 10.1016/j.bbamem.2019.183138] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Received: 09/24/2019] [Revised: 11/15/2019] [Accepted: 11/27/2019] [Indexed: 11/18/2022]
Abstract
A fluorescence ratiometric method utilizing the probe eosin Y is presented for estimating the ATP binding site polarity of P-type ATPases in different conformational states. The method has been calibrated by measurements in a series of alcohols and tested using complexation of eosin Y with methyl-β-cyclodextrin. The results obtained with the Na+,K+-, H+,K+- and sarcoplasmic reticulum Ca2+-ATPases indicate that the ATP binding site, to which eosin is known to bind, is significantly more polar in the case of the Na+,K+- and H+,K+-ATPases compared to the Ca2+-ATPase. This result was found to be consistent with docking calculations of eosin with the E2 conformational state of the Na+,K+-ATPase and the Ca2+-ATPase. Fluorescence experiments showed that eosin binds significantly more strongly to the E1 conformation of the Na+,K+-ATPase than the E2 conformation, but in the case of the Ca2+-ATPase both fluorescence experiments and docking calculations showed no significant difference in binding affinity between the two conformations. This result could be due to the fact that, in contrast to the Na+,K+- and H+,K+-ATPases, the E2-E1 transition of the Ca2+-ATPase does not involve the movement of a lysine-rich N-terminal tail which may affect the overall enzyme conformation. Consistent with this hypothesis, the eosin affinity of the E1 conformation of the Na+,K+-ATPase was significantly reduced after N-terminal truncation. It is suggested that changes in conformational entropy of the N-terminal tail of the Na+, K+- and the H+,K+-ATPases during the E2-E1 transition could affect the thermodynamic stability of the E1 conformation and hence its ATP binding affinity.
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Affiliation(s)
- K R Hossain
- School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia
| | - X Li
- School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia
| | - T Zhang
- Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA
| | - S Paula
- Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA
| | - F Cornelius
- Department of Biomedicine, University of Aarhus, DK-8000 Aarhus C, Denmark
| | - R J Clarke
- School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia; The University of Sydney Nano Institute, Sydney, NSW 2006, Australia.
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Garcia A, Lev B, Hossain KR, Gorman A, Diaz D, Pham THN, Cornelius F, Allen TW, Clarke RJ. Cholesterol depletion inhibits Na +,K +-ATPase activity in a near-native membrane environment. J Biol Chem 2019; 294:5956-5969. [PMID: 30770471 PMCID: PMC6463725 DOI: 10.1074/jbc.ra118.006223] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2018] [Revised: 02/08/2019] [Indexed: 12/28/2022] Open
Abstract
Cholesterol's effects on Na+,K+-ATPase reconstituted in phospholipid vesicles have been extensively studied. However, previous studies have reported both cholesterol-mediated stimulation and inhibition of Na+,K+-ATPase activity. Here, using partial reaction kinetics determined via stopped-flow experiments, we studied cholesterol's effect on Na+,K+-ATPase in a near-native environment in which purified membrane fragments were depleted of cholesterol with methyl-β-cyclodextrin (mβCD). The mβCD-treated Na+,K+-ATPase had significantly reduced overall activity and exhibited decreased observed rate constants for ATP phosphorylation (ENa3+ → E2P, i.e. phosphorylation by ATP and Na+ occlusion from the cytoplasm) and K+ deocclusion with subsequent intracellular Na+ binding (E2K2+ → E1Na3+). However, cholesterol depletion did not affect the observed rate constant for K+ occlusion by phosphorylated Na+,K+-ATPase on the extracellular face and subsequent dephosphorylation (E2P → E2K2+). Thus, partial reactions involving cation binding and release at the protein's intracellular side were most dependent on cholesterol. Fluorescence measurements with the probe eosin indicated that cholesterol depletion stabilizes the unphosphorylated E2 state relative to E1, and the cholesterol depletion-induced slowing of ATP phosphorylation kinetics was consistent with partial conversion of Na+,K+-ATPase into the E2 state, requiring a slow E2 → E1 transition before the phosphorylation. Molecular dynamics simulations of Na+,K+-ATPase in membranes with 40 mol % cholesterol revealed cholesterol interaction sites that differ markedly among protein conformations. They further indicated state-dependent effects on membrane shape, with the E2 state being likely disfavored in cholesterol-rich bilayers relative to the E1P state because of a greater hydrophobic mismatch. In summary, cholesterol extraction from membranes significantly decreases Na+,K+-ATPase steady-state activity.
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Affiliation(s)
- Alvaro Garcia
- From the School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia; The University of Sydney Nano Institute, Sydney, NSW 2006, Australia
| | - Bogdan Lev
- the School of Science, RMIT University, Melbourne, VIC 3001, Australia
| | - Khondker R Hossain
- From the School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia
| | - Amy Gorman
- From the School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia; the Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom
| | - Dil Diaz
- From the School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia
| | | | - Flemming Cornelius
- the Department of Biomedicine, University of Aarhus, DK-8000 Aarhus C, Denmark
| | - Toby W Allen
- the School of Science, RMIT University, Melbourne, VIC 3001, Australia; the Department of Chemistry, University of California, Davis, California 95616
| | - Ronald J Clarke
- From the School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia; The University of Sydney Nano Institute, Sydney, NSW 2006, Australia.
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Diaz D, Clarke RJ. Evolutionary Analysis of the Lysine-Rich N-terminal Cytoplasmic Domains of the Gastric H +,K +-ATPase and the Na +,K +-ATPase. J Membr Biol 2018; 251:653-666. [PMID: 30056551 DOI: 10.1007/s00232-018-0043-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2018] [Accepted: 07/19/2018] [Indexed: 12/16/2022]
Abstract
The catalytic α-subunits of both the Na+,K+-ATPase and the gastric H+,K+-ATPase possess lysine-rich N-termini which project into the cytoplasm. Due to conflicting experimental results, it is currently unclear whether the N-termini play a role in ion pump function or regulation, and, if they do, by what mechanism. Comparison of the lysine frequencies of the N-termini of both proteins with those of all of their extramembrane domains showed that the N-terminal lysine frequencies are far higher than one would expect simply from exposure to the aqueous solvent. The lysine frequency was found to vary significantly between different vertebrate classes, but this is due predominantly to a change in N-terminal length. As evidenced by a comparison between fish and mammals, an evolutionary trend towards an increase of the length of the N-terminus of the H+,K+-ATPase on going from an ancestral fish to mammals could be identified. This evolutionary trend supports the hypothesis that the N-terminus is important in ion pump function or regulation. In placental mammals, one of the lysines is replaced by serine (Ser-27), which is a target for protein kinase C. In most other animal species, a lysine occupies this position and hence no protein kinase C target is present. Interaction with protein kinase C is thus not the primary role of the lysine-rich N-terminus. The disordered structure of the N-terminus may, via increased flexibility, facilitate interaction with another binding partner, e.g. the surrounding membrane, or help to stabilise particular enzyme conformations via the increased entropy it produces.
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Affiliation(s)
- Dil Diaz
- School of Chemistry, University of Sydney, Sydney, NSW, 2006, Australia
| | - Ronald J Clarke
- School of Chemistry, University of Sydney, Sydney, NSW, 2006, Australia. .,The University of Sydney Nano Institute, Sydney, NSW, 2006, Australia.
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Interaction of N-terminal peptide analogues of the Na+,K+-ATPase with membranes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2018. [DOI: 10.1016/j.bbamem.2018.03.002] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Jiang Q, Garcia A, Han M, Cornelius F, Apell HJ, Khandelia H, Clarke RJ. Electrostatic Stabilization Plays a Central Role in Autoinhibitory Regulation of the Na +,K +-ATPase. Biophys J 2017; 112:288-299. [PMID: 28122215 DOI: 10.1016/j.bpj.2016.12.008] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2016] [Revised: 11/24/2016] [Accepted: 12/05/2016] [Indexed: 11/29/2022] Open
Abstract
The Na+,K+-ATPase is present in the plasma membrane of all animal cells. It plays a crucial role in maintaining the Na+ and K+ electrochemical potential gradients across the membrane, which are essential in numerous physiological processes, e.g., nerve, muscle, and kidney function. Its cellular activity must, therefore, be under tight metabolic control. Consideration of eosin fluorescence and stopped-flow kinetic data indicates that the enzyme's E2 conformation is stabilized by electrostatic interactions, most likely between the N-terminus of the protein's catalytic α-subunit and the adjacent membrane. The electrostatic interactions can be screened by increasing ionic strength, leading to a more evenly balanced equilibrium between the E1 and E2 conformations. This represents an ideal situation for effective regulation of the Na+,K+-ATPase's enzymatic activity, because protein modifications, which perturb this equilibrium in either direction, can then easily lead to activation or inhibition. The effect of ionic strength on the E1:E2 distribution and the enzyme's kinetics can be mathematically described by the Gouy-Chapman theory of the electrical double layer. Weakening of the electrostatic interactions and a shift toward E1 causes a significant increase in the rate of phosphorylation of the enzyme by ATP. Electrostatic stabilization of the Na+,K+-ATPase's E2 conformation, thus, could play an important role in regulating the enzyme's physiological catalytic turnover.
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Affiliation(s)
| | - Alvaro Garcia
- School of Chemistry, The University of Sydney, Sydney, New South Wales, Australia; Kolling Institute, University of Sydney, Sydney, New South Wales, Australia
| | - Minwoo Han
- MEMPHYS, Center for Biomembrane Physics, University of Southern Denmark, Odense, Denmark
| | | | | | - Himanshu Khandelia
- MEMPHYS, Center for Biomembrane Physics, University of Southern Denmark, Odense, Denmark
| | - Ronald J Clarke
- School of Chemistry, The University of Sydney, Sydney, New South Wales, Australia.
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Morth JP, Pedersen BP, Buch-Pedersen MJ, Andersen JP, Vilsen B, Palmgren MG, Nissen P. A structural overview of the plasma membrane Na+,K+-ATPase and H+-ATPase ion pumps. Nat Rev Mol Cell Biol 2011; 12:60-70. [PMID: 21179061 DOI: 10.1038/nrm3031] [Citation(s) in RCA: 244] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Plasma membrane ATPases are primary active transporters of cations that maintain steep concentration gradients. The ion gradients and membrane potentials derived from them form the basis for a range of essential cellular processes, in particular Na(+)-dependent and proton-dependent secondary transport systems that are responsible for uptake and extrusion of metabolites and other ions. The ion gradients are also both directly and indirectly used to control pH homeostasis and to regulate cell volume. The plasma membrane H(+)-ATPase maintains a proton gradient in plants and fungi and the Na(+),K(+)-ATPase maintains a Na(+) and K(+) gradient in animal cells. Structural information provides insight into the function of these two distinct but related P-type pumps.
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Affiliation(s)
- J Preben Morth
- Danish National Research Foundation, Centre for Membrane Pumps in Cells and Disease - PUMPKIN, Denmark
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