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Huang LK, Huang YC, Chen PC, Lee CH, Lin SM, Hsu YHH, Pan RL. Exploration of the Catalytic Cycle Dynamics of Vigna Radiata H +-Translocating Pyrophosphatases Through Hydrogen-Deuterium Exchange Mass Spectrometry. J Membr Biol 2023; 256:443-458. [PMID: 37955797 DOI: 10.1007/s00232-023-00295-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2023] [Accepted: 10/11/2023] [Indexed: 11/14/2023]
Abstract
Vigna radiata H+-translocating pyrophosphatases (VrH+-PPases, EC 3.6.1.1) are present in various endomembranes of plants, bacteria, archaea, and certain protozoa. They transport H+ into the lumen by hydrolyzing pyrophosphate, which is a by-product of many essential anabolic reactions. Although the crystal structure of H+-PPases has been elucidated, the H+ translocation mechanism of H+-PPases in the solution state remains unclear. In this study, we used hydrogen-deuterium exchange (HDX) coupled with mass spectrometry (MS) to investigate the dynamics of H+-PPases between the previously proposed R state (resting state, Apo form), I state (intermediate state, bound to a substrate analog), and T state (transient state, bound to inorganic phosphate). When hydrogen was replaced by proteins in deuterium oxide solution, the backbone hydrogen atoms, which were exchanged with deuterium, were identified through MS. Accordingly, we used deuterium uptake to examine the structural dynamics and conformational changes of H+-PPases in solution. In the highly conserved substrate binding and proton exit regions, HDX-MS revealed the existence of a compact conformation with deuterium exchange when H+-PPases were bound with a substrate analog and product. Thus, a novel working model was developed to elucidate the in situ catalytic mechanism of pyrophosphate hydrolysis and proton transport. In this model, a proton is released in the I state, and the TM5 inner wall serves as a proton piston.
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Affiliation(s)
- Li-Kun Huang
- Department of Life Science and Institute of Bioinformatics and Structural Biology, College of Life Science, National Tsing Hua University, No.101, Sec. 2, Kuangfu Rd., Hsinchu City, 30013, Taiwan, Republic of China
| | - Yi-Cyuan Huang
- Department of Chemistry, Tunghai University, No.1727, Sec. 4, Taiwan Boulevard, Taichung, 40704, Taiwan, Republic of China
| | - Pin-Chuan Chen
- Department of Life Science and Institute of Bioinformatics and Structural Biology, College of Life Science, National Tsing Hua University, No.101, Sec. 2, Kuangfu Rd., Hsinchu City, 30013, Taiwan, Republic of China
| | - Ching-Hung Lee
- Department of Life Science and Institute of Bioinformatics and Structural Biology, College of Life Science, National Tsing Hua University, No.101, Sec. 2, Kuangfu Rd., Hsinchu City, 30013, Taiwan, Republic of China
| | - Shih-Ming Lin
- Department of Biotechnology and Bioindustry Sciences, National Cheng Kung University, Tainan, 70101, Taiwan, Republic of China
| | - Yuan-Hao Howard Hsu
- Department of Chemistry, Tunghai University, No.1727, Sec. 4, Taiwan Boulevard, Taichung, 40704, Taiwan, Republic of China.
| | - Rong-Long Pan
- Department of Life Science and Institute of Bioinformatics and Structural Biology, College of Life Science, National Tsing Hua University, No.101, Sec. 2, Kuangfu Rd., Hsinchu City, 30013, Taiwan, Republic of China.
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Liao YY, Li JL, Pan RL, Chiou TJ. Structure-Function Analysis Reveals Amino Acid Residues of Arabidopsis Phosphate Transporter AtPHT1;1 Crucial for Its Activity. FRONTIERS IN PLANT SCIENCE 2019; 10:1158. [PMID: 31608095 PMCID: PMC6761603 DOI: 10.3389/fpls.2019.01158] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2019] [Accepted: 08/26/2019] [Indexed: 05/05/2023]
Abstract
Phosphorus (P), an essential plant macronutrient, is acquired in the form of inorganic phosphate (Pi) by transporters located at the plasma membrane of root cells. To decipher the Pi transport mechanism, Arabidopsis thaliana Pi transporter 1;1 (AtPHT1;1), the most predominantly H+-coupled Pi co-transporter in the root, was selected for structure-function analysis. We first predicted its secondary and tertiary structures on the basis of the Piriformospora indica Pi transporter (PiPT) and identified 28 amino acid residues potentially engaged in the activity of AtPHT1;1. We then mutagenized these residues into alanine and expressed them in the yeast pam2 mutant defective in high-affinity Pi transporters and Arabidopsis pht1;1 mutant, respectively, for functional complementation validation. We further incorporated the functional characterization and structure analyses to propose a mechanistic model for the function of AtPHT1;1. We showed that D35, D38, R134, and D144, implicated in H+ transfer across the membrane, and Y312 and N421, involved in initial interaction and translocation of Pi, are all essential for its transport activity. When Pi enters the binding pocket, the two aromatic moieties of Y145 and F169 and the hydrogen bonds generated from Q172, W304, Y312, D308, and K449 can build a scaffold to stabilize the structure. Subsequent interaction between Pi and the positive residue of K449 facilitates its release. Furthermore, D38, D93, R134, D144, D212, R216, R233, D367, K373, and E504 may form internal electrostatic interactions for structure ensemble and adaptability. This study offers a comprehensive model for elucidating the transport mechanism of a plant Pi transporter.
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Affiliation(s)
- Ya-Yun Liao
- Department of Life Science, Institute of Bioinformatics and Structural Biology, College of Life Science, National Tsing Hua University, Hsin Chu, Taiwan
| | - Jia-Ling Li
- Agricultural Biotechnology Research Center, Academia Sinica, Taipei, Taiwan
| | - Rong-Long Pan
- Department of Life Science, Institute of Bioinformatics and Structural Biology, College of Life Science, National Tsing Hua University, Hsin Chu, Taiwan
- *Correspondence: Tzyy-Jen Chiou, ; Rong-Long Pan,
| | - Tzyy-Jen Chiou
- Agricultural Biotechnology Research Center, Academia Sinica, Taipei, Taiwan
- *Correspondence: Tzyy-Jen Chiou, ; Rong-Long Pan,
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Strauss J, Wilkinson C, Vidilaseris K, Harborne SPD, Goldman A. A Simple Strategy to Determine the Dependence of Membrane-Bound Pyrophosphatases on K + as a Cofactor. Methods Enzymol 2018; 607:131-156. [PMID: 30149856 DOI: 10.1016/bs.mie.2018.04.018] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Membrane-bound pyrophosphatases (mPPases) couple pyrophosphate hydrolysis to H+ and/or Na+ pumping across membranes and are found in all domains of life except for multicellular animals including humans. They are important for development and stress resistance in plants. Furthermore, mPPases play a role in virulence of human pathogens that cause severe diseases such as malaria and African sleeping sickness. Sequence analysis, functional studies, and recently solved crystal structures have contributed to the understanding of the mPPase catalytic cycle. However, several key mechanistic features remain unknown. During evolution, several subgroups of mPPases differing in their pumping specificity and cofactor dependency arose. mPPases are classified into one of five subgroups, usually by sequence analysis. However, classification based solely on sequence has been inaccurate in several instances due to our limited understanding of the molecular mechanism of mPPases. Thus, pumping specificity and cofactor dependency of mPPases require experimental confirmation. Here, we describe a simple method for the determination of K+ dependency in mPPases using a hydrolytic activity assay. By coupling these dependency studies with site-directed mutagenesis, we have begun to build a better understanding of the molecular mechanisms of mPPases. We optimized the assay for thermostable mPPases that are commonly used as model systems in our lab, but the method is equally applicable to mesophilic mPPases with minor modifications.
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Affiliation(s)
- Jannik Strauss
- Astbury Centre for Structural Biology, University of Leeds, Leeds, United Kingdom
| | - Craig Wilkinson
- Astbury Centre for Structural Biology, University of Leeds, Leeds, United Kingdom
| | - Keni Vidilaseris
- Faculty of Biological and Environmental Sciences, University of Helsinki, Helsinki, Finland
| | - Steven P D Harborne
- Astbury Centre for Structural Biology, University of Leeds, Leeds, United Kingdom.
| | - Adrian Goldman
- Astbury Centre for Structural Biology, University of Leeds, Leeds, United Kingdom; Faculty of Biological and Environmental Sciences, University of Helsinki, Helsinki, Finland.
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Membrane pyrophosphatases from Thermotoga maritima and Vigna radiata suggest a conserved coupling mechanism. Nat Commun 2016; 7:13596. [PMID: 27922000 PMCID: PMC5150537 DOI: 10.1038/ncomms13596] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2015] [Accepted: 10/18/2016] [Indexed: 11/08/2022] Open
Abstract
Membrane-bound pyrophosphatases (M-PPases), which couple proton/sodium ion transport to pyrophosphate synthesis/hydrolysis, are important in abiotic stress resistance and in the infectivity of protozoan parasites. Here, three M-PPase structures in different catalytic states show that closure of the substrate-binding pocket by helices 5-6 affects helix 13 in the dimer interface and causes helix 12 to move down. This springs a 'molecular mousetrap', repositioning a conserved aspartate and activating the nucleophilic water. Corkscrew motion at helices 6 and 16 rearranges the key ionic gate residues and leads to ion pumping. The pumped ion is above the ion gate in one of the ion-bound structures, but below it in the other. Electrometric measurements show a single-turnover event with a non-hydrolysable inhibitor, supporting our model that ion pumping precedes hydrolysis. We propose a complete catalytic cycle for both proton and sodium-pumping M-PPases, and one that also explains the basis for ion specificity.
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Chen YW, Lee CH, Huang YT, Pan YJ, Lin SM, Lo YY, Lee CH, Huang LK, Huang YF, Hsu YD, Pan RL. Functional and fluorescence analyses of tryptophan residues in H+-pyrophosphatase of Clostridium tetani. J Bioenerg Biomembr 2015; 46:127-34. [PMID: 24121937 DOI: 10.1007/s10863-013-9532-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2013] [Accepted: 10/01/2013] [Indexed: 10/26/2022]
Abstract
Homodimeric proton-translocating pyrophosphatase (H+-PPase; EC 3.6.1.1) maintains the cytoplasmic pH homeostasis of many bacteria and higher plants by coupling pyrophosphate (PPi) hydrolysis and proton translocation. H+-PPase accommodates several essential motifs involved in the catalytic mechanism, including the PPi binding motif and Acidic I and II motifs. In this study, 3 intrinsic tryptophan residues, Trp-75, Trp-365, and Trp-602, in H+-PPase from Clostridium tetani were used as internal probes to monitor the local conformational state of the periplasm domain, transmembrane region, and cytoplasmic domain, respectively. Upon binding of the substrate analog Mg-imidodiphosphate (Mg-IDP), local structural changes prevented the modification of tryptophan residues by N-bromosuccinimide (NBS), especially at Trp-602. Following Mg-Pi binding, Trp-75 and Trp-365, but not Trp-602, were slightly protected from structural modifications by NBS. These results reveal the conformation of H+-PPase is distinct in the presence of different ligands. Moreover, analyses of the Stern-Volmer relationship and steady-state fluorescence anisotropy also indicate that the local structure around Trp-602 is more exposed to solvent and varied under different environments. In addition, Trp-602 was identified to be a crucial residue in the H+-PPase that may potentially be involved in stabilizing the structure of the catalytic region by site-directed mutagenesis analysis.
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Hsu SH, Lo YY, Liu TH, Pan YJ, Huang YT, Sun YJ, Hung CC, Tseng FG, Yang CW, Pan RL. Substrate-induced changes in domain interaction of vacuolar H⁺-pyrophosphatase. J Biol Chem 2015; 290:1197-209. [PMID: 25451931 DOI: 10.1074/jbc.m114.568139] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Single molecule atomic force microscopy (smAFM) was employed to unfold transmembrane domain interactions of a unique vacuolar H(+)-pyrophosphatase (EC 3.6.1.1) from Vigna radiata. H(+)-Pyrophosphatase is a membrane-embedded homodimeric protein containing a single type of polypeptide and links PPi hydrolysis to proton translocation. Each subunit consists of 16 transmembrane domains with both ends facing the lumen side. In this investigation, H(+)-pyrophosphatase was reconstituted into the lipid bilayer in the same orientation for efficient fishing out of the membrane by smAFM. The reconstituted H(+)-pyrophosphatase in the lipid bilayer showed an authentically dimeric structure, and the size of each monomer was ∼4 nm in length, ∼2 nm in width, and ∼1 nm in protrusion height. Upon extracting the H(+)-pyrophosphatase out of the membrane, force-distance curves containing 10 peaks were obtained and assigned to distinct domains. In the presence of pyrophosphate, phosphate, and imidodiphosphate, the numbers of interaction curves were altered to 7, 8, and 10, respectively, concomitantly with significant modification in force strength. The substrate-binding residues were further replaced to verify these domain changes upon substrate binding. A working model is accordingly proposed to show the interactions between transmembrane domains of H(+)-pyrophosphatase in the presence and absence of substrate and its analog.
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Affiliation(s)
- Shen-Hsing Hsu
- From the Department of Nephrology, Kidney Research Center, Chang Gung Memorial Hospital, Chang Gung University College of Medicine, Taoyuan 33333
| | - Yueh-Yu Lo
- From the Department of Nephrology, Kidney Research Center, Chang Gung Memorial Hospital, Chang Gung University College of Medicine, Taoyuan 33333
| | - Tseng-Huang Liu
- the Department of Life Science and Institute of Bioinformatics and Structural Biology, College of Life Science, and
| | - Yih-Jiuan Pan
- the Department of Life Science and Institute of Bioinformatics and Structural Biology, College of Life Science, and
| | - Yun-Tzu Huang
- the Department of Life Science and Institute of Bioinformatics and Structural Biology, College of Life Science, and
| | - Yuh-Ju Sun
- the Department of Life Science and Institute of Bioinformatics and Structural Biology, College of Life Science, and
| | - Cheng-Chieh Hung
- From the Department of Nephrology, Kidney Research Center, Chang Gung Memorial Hospital, Chang Gung University College of Medicine, Taoyuan 33333
| | - Fan-Gang Tseng
- Department of Engineering and System Science, College of Nuclear Science, National Tsing Hua University, Hsin Chu 30013, Taiwan
| | - Chih-Wei Yang
- From the Department of Nephrology, Kidney Research Center, Chang Gung Memorial Hospital, Chang Gung University College of Medicine, Taoyuan 33333,
| | - Rong-Long Pan
- the Department of Life Science and Institute of Bioinformatics and Structural Biology, College of Life Science, and
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Asaoka M, Segami S, Maeshima M. Identification of the critical residues for the function of vacuolar H+-pyrophosphatase by mutational analysis based on the 3D structure. ACTA ACUST UNITED AC 2014; 156:333-44. [DOI: 10.1093/jb/mvu046] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
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Lee CH, Chen YW, Huang YT, Pan YJ, Lee CH, Lin SM, Huang LK, Lo YY, Huang YF, Hsu YD, Yen SC, Hwang JK, Pan RL. Functional Investigation of Transmembrane Helix 3 in H+-Translocating Pyrophosphatase. J Membr Biol 2013; 246:959-66. [DOI: 10.1007/s00232-013-9599-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2013] [Accepted: 09/24/2013] [Indexed: 10/26/2022]
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Wang Y, Jin S, Wang M, Zhu L, Zhang X. Isolation and characterization of a conserved domain in the eremophyte H+-PPase family. PLoS One 2013; 8:e70099. [PMID: 23922918 PMCID: PMC3726567 DOI: 10.1371/journal.pone.0070099] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2013] [Accepted: 06/14/2013] [Indexed: 11/24/2022] Open
Abstract
H+-translocating inorganic pyrophosphatases (H+-PPase) were recognized as the original energy donors in the development of plants. A large number of researchers have shown that H+-PPase could be an early-originated protein that participated in many important biochemical and physiological processes. In this study we cloned 14 novel sequences from 7 eremophytes: Sophora alopecuroid (Sa), Glycyrrhiza uralensis (Gu), Glycyrrhiza inflata (Gi), Suaeda salsa (Ss), Suaeda rigida (Sr), Halostachys caspica (Hc), and Karelinia caspia (Kc). These novel sequences included 6 ORFs and 8 fragments, and they were identified as H+-PPases based on the typical conserved domains. Besides the identified domains, sequence alignment showed that there still were two novel conserved motifs. A phylogenetic tree was constructed, including the 14 novel H+-PPase amino acid sequences and the other 34 identified H+-PPase protein sequences representing plants, algae, protozoans and bacteria. It was shown that these 48 H+-PPases were classified into two groups: type I and type II H+-PPase. The novel 14 eremophyte H+-PPases were classified into the type I H+-PPase. The 3D structures of these H+-PPase proteins were predicted, which suggested that all type I H+-PPases from higher plants and algae were homodimers, while other type I H+-PPases from bacteria and protozoans and all type II H+-PPases were monomers. The 3D structures of these novel H+-PPases were homodimers except for SaVP3, which was a monomer. This regular structure could provide important evidence for the evolutionary origin and study of the relationship between the structure and function among members of the H+-PPase family.
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Affiliation(s)
- Yanqin Wang
- National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan, Hubei, China
- College of Life Science, Tarim University, Alaer, Xinjiang, China
| | - Shuangxia Jin
- National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan, Hubei, China
| | - Maojun Wang
- National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan, Hubei, China
| | - Longfu Zhu
- National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan, Hubei, China
- * E-mail:
| | - Xianlong Zhang
- National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan, Hubei, China
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Huang YT, Liu TH, Lin SM, Chen YW, Pan YJ, Lee CH, Sun YJ, Tseng FG, Pan RL. Squeezing at entrance of proton transport pathway in proton-translocating pyrophosphatase upon substrate binding. J Biol Chem 2013; 288:19312-20. [PMID: 23720778 DOI: 10.1074/jbc.m113.469353] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Homodimeric proton-translocating pyrophosphatase (H(+)-PPase; EC 3.6.1.1) is indispensable for many organisms in maintaining organellar pH homeostasis. This unique proton pump couples the hydrolysis of PPi to proton translocation across the membrane. H(+)-PPase consists of 14-16 relatively hydrophobic transmembrane domains presumably for proton translocation and hydrophilic loops primarily embedding a catalytic site. Several highly conserved polar residues located at or near the entrance of the transport pathway in H(+)-PPase are essential for proton pumping activity. In this investigation single molecule FRET was employed to dissect the action at the pathway entrance in homodimeric Clostridium tetani H(+)-PPase upon ligand binding. The presence of the substrate analog, imidodiphosphate mediated two sites at the pathway entrance moving toward each other. Moreover, single molecule FRET analyses after the mutation at the first proton-carrying residue (Arg-169) demonstrated that conformational changes at the entrance are conceivably essential for the initial step of H(+)-PPase proton translocation. A working model is accordingly proposed to illustrate the squeeze at the entrance of the transport pathway in H(+)-PPase upon substrate binding.
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Affiliation(s)
- Yun-Tzu Huang
- Department of Life Science and Institute of Bioinformatics and Structural Biology, National Tsing Hua University, Hsin Chu 30013, Taiwan
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Kajander T, Kellosalo J, Goldman A. Inorganic pyrophosphatases: one substrate, three mechanisms. FEBS Lett 2013; 587:1863-9. [PMID: 23684653 DOI: 10.1016/j.febslet.2013.05.003] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2013] [Accepted: 05/06/2013] [Indexed: 10/26/2022]
Abstract
Soluble inorganic pyrophosphatases (PPases) catalyse an essential reaction, the hydrolysis of pyrophosphate to inorganic phosphate. In addition, an evolutionarily ancient family of membrane-integral pyrophosphatases couple this hydrolysis to Na(+) and/or H(+) pumping, and so recycle some of the free energy from the pyrophosphate. The structures of the H(+)-pumping mung bean PPase and the Na(+)-pumping Thermotoga maritima PPase solved last year revealed an entirely novel membrane protein containing 16 transmembrane helices. The hydrolytic centre, well above the membrane, is linked by a charged "coupling funnel" to the ionic gate about 20Å away. By comparing the active sites, fluoride inhibition data and the various models for ion transport, we conclude that membrane-integral PPases probably use binding of pyrophosphate to drive pumping.
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Affiliation(s)
- Tommi Kajander
- Institute of Biotechnology, University of Helsinki, Helsinki, Finland.
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Kellosalo J, Kajander T, Kogan K, Pokharel K, Goldman A. The structure and catalytic cycle of a sodium-pumping pyrophosphatase. Science 2012; 337:473-6. [PMID: 22837527 DOI: 10.1126/science.1222505] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Membrane-integral pyrophosphatases (M-PPases) are crucial for the survival of plants, bacteria, and protozoan parasites. They couple pyrophosphate hydrolysis or synthesis to Na(+) or H(+) pumping. The 2.6-angstrom structure of Thermotoga maritima M-PPase in the resting state reveals a previously unknown solution for ion pumping. The hydrolytic center, 20 angstroms above the membrane, is coupled to the gate formed by the conserved Asp(243), Glu(246), and Lys(707) by an unusual "coupling funnel" of six α helices. Comparison with our 4.0-angstrom resolution structure of the product complex suggests that helix 12 slides down upon substrate binding to open the gate by a simple binding-change mechanism. Below the gate, four helices form the exit channel. Superimposing helices 3 to 6, 9 to 12, and 13 to 16 suggests that M-PPases arose through gene triplication.
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Affiliation(s)
- Juho Kellosalo
- Structural Biology and Biophysics Program, Institute of Biotechnology, Post Office Box 65, University of Helsinki, FIN-00014, Finland
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Crystal structure of a membrane-embedded H+-translocating pyrophosphatase. Nature 2012; 484:399-403. [PMID: 22456709 DOI: 10.1038/nature10963] [Citation(s) in RCA: 104] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2011] [Accepted: 02/17/2012] [Indexed: 11/08/2022]
Abstract
H(+)-translocating pyrophosphatases (H(+)-PPases) are active proton transporters that establish a proton gradient across the endomembrane by means of pyrophosphate (PP(i)) hydrolysis. H(+)-PPases are found primarily as homodimers in the vacuolar membrane of plants and the plasma membrane of several protozoa and prokaryotes. The three-dimensional structure and detailed mechanisms underlying the enzymatic and proton translocation reactions of H(+)-PPases are unclear. Here we report the crystal structure of a Vigna radiata H(+)-PPase (VrH(+)-PPase) in complex with a non-hydrolysable substrate analogue, imidodiphosphate (IDP), at 2.35 Å resolution. Each VrH(+)-PPase subunit consists of an integral membrane domain formed by 16 transmembrane helices. IDP is bound in the cytosolic region of each subunit and trapped by numerous charged residues and five Mg(2+) ions. A previously undescribed proton translocation pathway is formed by six core transmembrane helices. Proton pumping can be initialized by PP(i) hydrolysis, and H(+) is then transported into the vacuolar lumen through a pathway consisting of Arg 242, Asp 294, Lys 742 and Glu 301. We propose a working model of the mechanism for the coupling between proton pumping and PP(i) hydrolysis by H(+)-PPases.
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