1
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Ma XC, Wang K, Gao XL, Li XK, Liu GG, Chen HY, Piao CY, You SJ. Deciphering the fate of osmotic stress priming on enhanced microorganism acclimation for purified terephthalic acid wastewater treatment with high salinity and organic load. BIORESOURCE TECHNOLOGY 2023; 374:128656. [PMID: 36690216 DOI: 10.1016/j.biortech.2023.128656] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2022] [Revised: 01/16/2023] [Accepted: 01/18/2023] [Indexed: 06/17/2023]
Abstract
Osmotic stress priming (OSP) was an effective management strategy for improving microbial acclimation to salt stress. In this study, the interaction between pollutants and microbiota, and microbial osmoregulation were investigated triggered by OSP (alternately increasing salinity and organic loading). Results showed that OSP significantly improved COD removal from 31.53 % to 67.99 % and mitigated the terephthalate inhibition produced by toluate, decreasing from 1908.08 mg/L to 837.16 mg/L compared with direct priming. Due to an increase in salinity, Pelotomaculum and Mesotoga were enriched to facilitate terephthalate degradation and syntrophic acetate oxidation (SAO). And organic load promoted acetate formation through syntrophic metabolism of Syntrophorhabdus/Pelotomaculum and SAO-dependent hydrogenotrophic methanogenesis. K+ absorbing, proline and trehalose synthesis participated in osmoregulation at 0.5 % salinity, while only ectoine alleviated intracellular osmolarity under 1.0 % salinity with OLR of 0.44 kg COD /m3. This study provided in-depth insight for microbial acclimation process of anaerobic priming of saline wastewater.
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Affiliation(s)
- Xiao-Chen Ma
- State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, China
| | - Ke Wang
- State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, China; National Engineering Research Center for Safe Sludge Disposal and Resource Recovery, Harbin Institute of Technology, Harbin 150090, China; Harbin Institute of Technology National Engineering Research Center of Water Resources Co., Ltd, Guangdong Yuehai Water Investment Co., Ltd, Harbin 150090, China
| | - Xin-Lei Gao
- Harbin Institute of Technology National Engineering Research Center of Water Resources Co., Ltd, Guangdong Yuehai Water Investment Co., Ltd, Harbin 150090, China
| | - Xiang-Kun Li
- School of Civil and Transportation, Hebei University of Technology, Tianjin 300401, China.
| | - Gai-Ge Liu
- School of Civil and Transportation, Hebei University of Technology, Tianjin 300401, China
| | - Hong-Ying Chen
- State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, China
| | - Chen-Yu Piao
- State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, China
| | - Shi-Jie You
- State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, China
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2
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Deciphering ion transport and ATPase coupling in the intersubunit tunnel of KdpFABC. Nat Commun 2021; 12:5098. [PMID: 34429416 PMCID: PMC8385062 DOI: 10.1038/s41467-021-25242-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2021] [Accepted: 07/29/2021] [Indexed: 02/07/2023] Open
Abstract
KdpFABC, a high-affinity K+ pump, combines the ion channel KdpA and the P-type ATPase KdpB to secure survival at K+ limitation. Here, we apply a combination of cryo-EM, biochemical assays, and MD simulations to illuminate the mechanisms underlying transport and the coupling to ATP hydrolysis. We show that ions are transported via an intersubunit tunnel through KdpA and KdpB. At the subunit interface, the tunnel is constricted by a phenylalanine, which, by polarized cation-π stacking, controls K+ entry into the canonical substrate binding site (CBS) of KdpB. Within the CBS, ATPase coupling is mediated by the charge distribution between an aspartate and a lysine. Interestingly, individual elements of the ion translocation mechanism of KdpFABC identified here are conserved among a wide variety of P-type ATPases from different families. This leads us to the hypothesis that KdpB might represent an early descendant of a common ancestor of cation pumps.
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3
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Stautz J, Hellmich Y, Fuss MF, Silberberg JM, Devlin JR, Stockbridge RB, Hänelt I. Molecular Mechanisms for Bacterial Potassium Homeostasis. J Mol Biol 2021; 433:166968. [PMID: 33798529 DOI: 10.1016/j.jmb.2021.166968] [Citation(s) in RCA: 48] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2021] [Revised: 03/11/2021] [Accepted: 03/22/2021] [Indexed: 10/21/2022]
Abstract
Potassium ion homeostasis is essential for bacterial survival, playing roles in osmoregulation, pH homeostasis, regulation of protein synthesis, enzyme activation, membrane potential adjustment and electrical signaling. To accomplish such diverse physiological tasks, it is not surprising that a single bacterium typically encodes several potassium uptake and release systems. To understand the role each individual protein fulfills and how these proteins work in concert, it is important to identify the molecular details of their function. One needs to understand whether the systems transport ions actively or passively, and what mechanisms or ligands lead to the activation or inactivation of individual systems. Combining mechanistic information with knowledge about the physiology under different stress situations, such as osmostress, pH stress or nutrient limitation, one can identify the task of each system and deduce how they are coordinated with each other. By reviewing the general principles of bacterial membrane physiology and describing the molecular architecture and function of several bacterial K+-transporting systems, we aim to provide a framework for microbiologists studying bacterial potassium homeostasis and the many K+-translocating systems that are still poorly understood.
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Affiliation(s)
- Janina Stautz
- Institute of Biochemistry, Goethe University Frankfurt, Frankfurt am Main, Germany
| | - Yvonne Hellmich
- Institute of Biochemistry, Goethe University Frankfurt, Frankfurt am Main, Germany
| | - Michael F Fuss
- Institute of Biochemistry, Goethe University Frankfurt, Frankfurt am Main, Germany
| | - Jakob M Silberberg
- Institute of Biochemistry, Goethe University Frankfurt, Frankfurt am Main, Germany
| | - Jason R Devlin
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, United States
| | - Randy B Stockbridge
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, United States.
| | - Inga Hänelt
- Institute of Biochemistry, Goethe University Frankfurt, Frankfurt am Main, Germany.
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4
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Abstract
In bacteria, K+ is used to maintain cell volume and osmotic potential. Homeostasis normally involves a network of constitutively expressed transport systems, but in K+ deficient environments, the KdpFABC complex uses ATP to pump K+ into the cell. This complex appears to be a hybrid of two types of transporters, with KdpA descending from the superfamily of K+ transporters and KdpB belonging to the superfamily of P-type ATPases. Studies of enzymatic activity documented a catalytic cycle with hallmarks of classical P-type ATPases and studies of ion transport indicated that K+ import into the cytosol occurred in the second half of this cycle in conjunction with hydrolysis of an aspartyl phosphate intermediate. Atomic structures of the KdpFABC complex from X-ray crystallography and cryo-EM have recently revealed conformations before and after formation of this aspartyl phosphate that appear to contradict the functional studies. Specifically, structural comparisons with the archetypal P-type ATPase, SERCA, suggest that K+ transport occurs in the first half of the cycle, accompanying formation of the aspartyl phosphate. Further controversy has arisen regarding the path by which K+ crosses the membrane. The X-ray structure supports the conventional view that KdpA provides the conduit, whereas cryo-EM structures suggest that K+ moves from KdpA through a long, intramembrane tunnel to reach canonical ion binding sites in KdpB from which they are released to the cytosol. This review discusses evidence supporting these contradictory models and identifies key experiments needed to resolve discrepancies and produce a unified model for this fascinating mechanistic hybrid.
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Affiliation(s)
- Bjørn P Pedersen
- a Department of Molecular Biology and Genetics, Aarhus University , Aarhus C , Denmark
| | - David L Stokes
- b Department of Cell Biology, New York University School of Medicine, Skirball Institute , New York , NY , USA
| | - Hans-Jürgen Apell
- c Department of Biology, University of Konstanz , Konstanz , Germany
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5
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Cryo-EM structures of KdpFABC suggest a K + transport mechanism via two inter-subunit half-channels. Nat Commun 2018; 9:4971. [PMID: 30478378 PMCID: PMC6255902 DOI: 10.1038/s41467-018-07319-2] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2018] [Accepted: 10/24/2018] [Indexed: 12/16/2022] Open
Abstract
P-type ATPases ubiquitously pump cations across biological membranes to maintain vital ion gradients. Among those, the chimeric K+ uptake system KdpFABC is unique. While ATP hydrolysis is accomplished by the P-type ATPase subunit KdpB, K+ has been assumed to be transported by the channel-like subunit KdpA. A first crystal structure uncovered its overall topology, suggesting such a spatial separation of energizing and transporting units. Here, we report two cryo-EM structures of the 157 kDa, asymmetric KdpFABC complex at 3.7 Å and 4.0 Å resolution in an E1 and an E2 state, respectively. Unexpectedly, the structures suggest a translocation pathway through two half-channels along KdpA and KdpB, uniting the alternating-access mechanism of actively pumping P-type ATPases with the high affinity and selectivity of K+ channels. This way, KdpFABC would function as a true chimeric complex, synergizing the best features of otherwise separately evolved transport mechanisms.
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6
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Abstract
Cellular potassium import systems play a fundamental role in osmoregulation, pH homeostasis and membrane potential in all domains of life. In bacteria, the kdp operon encodes a four subunit potassium pump that maintains intracellular homeostasis as well as cell shape and turgor under conditions where potassium is limiting1. This membrane complex, called KdpFABC, has one channel-like subunit (KdpA) belonging to the Superfamily of Potassium Transporters and another pump-like subunit (KdpB) belonging to the Superfamily of P-type ATPases. Although there is considerable structural and functional information about members from both superfamilies, the mechanism by which uphill potassium transport through KdpA is coupled with ATP hydrolysis by KdpB remains poorly understood. Here we report the 2.9 Å X-ray structure of the complete Escherichia coli KdpFABC complex with a potassium ion within the selectivity filter of KdpA as well as a water molecule at a canonical cation site in the transmembrane domain of KdpB. The structure also reveals two structural elements that appear to mediate the coupling between these two subunits. Specifically, a protein-embedded tunnel runs between these potassium and water sites and a helix controlling the cytoplasmic gate of KdpA is linked to the phosphorylation domain of KdpB. Based on these observations, we propose an unprecedented mechanism that repurposes protein channel architecture for active transport across biomembranes.
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Affiliation(s)
- Ching-Shin Huang
- Molecular Biophysics Graduate Program, New York University School of Medicine, Skirball Institute, 540 First Avenue, New York, New York 10016, USA
| | - Bjørn Panyella Pedersen
- Department of Molecular Biology and Genetics, Aarhus University, Gustav Wieds Vej 10, DK-8000 Aarhus C, Denmark.,Aarhus Institute of Advanced Studies, Aarhus University, Høegh-Guldbergs Gade 6B, DK-8000 Aarhus C, Denmark
| | - David L Stokes
- Department of Cell Biology, New York University School of Medicine, Skirball Institute, 540 First Avenue, New York, New York 10016, USA
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7
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Bräuer S, Cadillo-Quiroz H, Kyrpides N, Woyke T, Goodwin L, Detter C, Podell S, Yavitt JB, Zinder SH. Genome of Methanoregula boonei 6A8 reveals adaptations to oligotrophic peatland environments. MICROBIOLOGY-SGM 2015; 161:1572-1581. [PMID: 25998264 DOI: 10.1099/mic.0.000117] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Analysis of the genome sequence of Methanoregula boonei strain 6A8, an acidophilic methanogen isolated from an ombrotrophic (rain-fed) peat bog, has revealed unique features that likely allow it to survive in acidic, nutrient-poor conditions. First, M. boonei is predicted to generate ATP using protons that are abundant in peat, rather than sodium ions that are scarce, and the sequence of a membrane-bound methyltransferase, believed to pump Na+ in all methanogens, shows differences in key amino acid residues. Further, perhaps reflecting the hypokalemic status of many peat bogs, M. boonei demonstrates redundancy in the predicted potassium uptake genes trk, kdp and kup, some of which may have been horizontally transferred to methanogens from bacteria, possibly Geobacter spp. Overall, the putative functions of the potassium uptake, ATPase and methyltransferase genes may, at least in part, explain the cosmopolitan success of group E1/E2 and related methanogenic archaea in acidic peat bogs.
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Affiliation(s)
- Suzanna Bräuer
- Department of Biology, Appalachian State University, Boone, NC 28608, USA
| | - Hinsby Cadillo-Quiroz
- Swette Center for Environmental Biotechnology at the Biodesign Institute, Arizona State University, Tempe, AZ 85287-4501, USA
| | - Nikos Kyrpides
- Department of Energy, Joint Genome Institute, Walnut Creek, CA 94598, USA
| | - Tanja Woyke
- Department of Energy, Joint Genome Institute, Walnut Creek, CA 94598, USA
| | - Lynne Goodwin
- Los Alamos National Laboratory, Los Alamos, NM 87545, USA
| | - Chris Detter
- Los Alamos National Laboratory, Los Alamos, NM 87545, USA
| | - Sheila Podell
- Scripps Institution of Oceanography, La Jolla, CA 92093, USA
| | - Joseph B Yavitt
- Department of Natural Resources, Cornell University, Ithaca, NY 14853, USA
| | - Stephen H Zinder
- Department of Microbiology, Cornell University, Ithaca, NY 14853, USA
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8
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Damnjanovic B, Apell HJ. KdpFABC reconstituted in Escherichia coli lipid vesicles: substrate dependence of the transport rate. Biochemistry 2014; 53:5674-82. [PMID: 25144826 DOI: 10.1021/bi5008244] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
KdpFABC complexes were reconstituted in Escherichia coli lipid vesicles, and ion pumping was activated by addition of ATP to the external medium which corresponds to the cytoplasm under physiological conditions. ATP-driven potassium extrusion was studied in the presence of various substrates potentially influencing transport rate. The pump current was detected as a decrease of the membrane potential by the voltage-sensitive dye DiSC3(5). The results indicate that high cytoplasmic K(+) concentrations have an inhibitory effect on the KdpFABC complex. The pump current decreased to ∼25% of the maximal value at 140 mM K(+) and minimal Mg(2+)concentrations. This effect could be counteracted with increased Mg(2+) concentrations on the cytoplasmic side. This observation may be explained by the Gouy-Chapman effect of two Mg(2+) ions probably bound with a K1/2 of 0.8 mM close to the entrance of the access channel to the binding sites. This factor ensures that under physiological conditions the rate-limiting effect of K(+) release is significantly reduced. Also both ADP and inorganic phosphate are able to reduce the turnover rate of the pump by reversing the phosphorylation step (Ki of 151 μM) and the dephosphorylation step (Ki of 268 μM), respectively. In the case of the DDM-solubilized KdpFABC complex, activation energy under turnover conditions was previously found to be 55 kJ/mol, and the o-vanadate inhibition constant is shown here to be ∼1 μM, which is in agreement with values reported for other P-type ATPases. In the case of the reconstituted enzyme, however, significant differences were observed that have to be assigned to effects of the lipid bilayer environment. The activation energy was increased by a factor of 2, whereas the inhibition by o-vanadate became reduced in a way that only ∼66% of the enzyme could be inhibited and the inhibition constant was increased to a value of ∼60 μM.
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Affiliation(s)
- Bojana Damnjanovic
- Department of Biology and Konstanz Research School Chemical Biology, University of Konstanz , 78464 Konstanz, Germany
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9
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Damnjanovic B, Apell HJ. Role of protons in the pump cycle of KdpFABC investigated by time-resolved kinetic experiments. Biochemistry 2014; 53:3218-28. [PMID: 24766073 DOI: 10.1021/bi500336w] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The time-resolved kinetics of the KdpFABC complex solubilized in Aminoxide WS-35 was investigated by ATP concentration jump experiments. ATP was photoreleased from its inactive precursor, caged ATP, and charge movements in the membrane domain of the KdpFABC were detected by the electrochromic dye RH421. At low ATP concentrations, the ATP binding step became rate-limiting with an apparent, pH-independent ATP binding affinity of ~70 μM. At saturating ATP concentrations, the rate-limiting step is the conformational transition (E1-P → P-E2) with a rate constant of ~1.7 s(-1) at 20 °C that was independent of K(+) concentration. This observation together with the detected fluorescence decrease indicates that K(+) (or another positive ion) is bound in the membrane domain after enzyme phosphorylation and the conformational transition to the P-E2 state. pH dependence experiments revealed different roles of H(+) in the transport mechanism. Two different functions of protons for the ion pump must be distinguished. On one hand, there are electrogenically bound "functional" protons, which are not transported but prerequisite for the performance of the ATP-driven half-cycle. On the other hand, protons bind to the transport sites, acting as weak congeners of K(+). There possibly are noncompetitively bound protons, affecting the enzyme activity and/or coupling between KdpA and KdpB subunits. Finally, the recently proposed Post-Albers model for the KdpFABC complex was supplemented with stoichiometry factors of 2 for K(+) and 3 for H(+), and additional inhibitory side reactions controlled by H(+) were introduced, which are relevant at pH <6.5 and/or in the absence of K(+).
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10
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Damnjanovic B, Weber A, Potschies M, Greie JC, Apell HJ. Mechanistic analysis of the pump cycle of the KdpFABC P-type ATPase. Biochemistry 2013; 52:5563-76. [PMID: 23930894 DOI: 10.1021/bi400729e] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The high-affinity potassium uptake system KdpFABC is a unique type Ia P-type ATPase, because it separates the sites of ATP hydrolysis and ion transport on two different subunits. KdpFABC was expressed in Escherichia coli. It was then isolated and purified to homogeneity to obtain a detergent-solubilized enzyme complex that allowed the analysis of ion binding properties. The electrogenicity and binding affinities of the ion pump for K(+) and H(+) were determined in detergent-solubilized complexes by means of the electrochromic styryl dye RH421. Half-saturating K(+) concentrations and pK values for H(+) binding could be obtained in both the unphosphorylated and phosphorylated conformations of KdpFABC. The interaction of both ions with KdpFABC was studied in detail, and the presence of independent binding sites was ascertained. It is proposed that KdpFABC reconstituted in vesicles translocates protons at a low efficiency opposite from the well-established import of K(+) into the bacteria. On the basis of our results, various mechanistic pump cycle models were derived from the general Post-Albers scheme of P-type ATPases and discussed in the framework of the experimental evidence to propose a possible molecular pump cycle for KdpFABC.
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11
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Affiliation(s)
- Michael G. Palmgren
- Center for Membrane Pumps in Cells and Disease – PUMPKIN, Danish National Research Foundation, University of Copenhagen, DK-1871 Frederiksberg C, Denmark;
| | - Poul Nissen
- Center for Membrane Pumps in Cells and Disease – PUMPKIN, Danish National Research Foundation, Aarhus University, DK-8000 Århus C, Denmark;
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12
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Becker D, Fendler K, Altendorf K, Greie JC. The Conserved Dipole in Transmembrane Helix 5 of KdpB in the Escherichia coli KdpFABC P-Type ATPase Is Crucial for Coupling and the Electrogenic K+-Translocation Step. Biochemistry 2007; 46:13920-8. [DOI: 10.1021/bi701394h] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Doris Becker
- Abteilung Mikrobiologie, Fachbereich Biologie/Chemie, Universität Osnabrück, 49069 Osnabrück, and Max Planck Institut für Biophysik, Max-von-Laue-Strasse 3, 60438 Frankfurt/Main, Germany
| | - Klaus Fendler
- Abteilung Mikrobiologie, Fachbereich Biologie/Chemie, Universität Osnabrück, 49069 Osnabrück, and Max Planck Institut für Biophysik, Max-von-Laue-Strasse 3, 60438 Frankfurt/Main, Germany
| | - Karlheinz Altendorf
- Abteilung Mikrobiologie, Fachbereich Biologie/Chemie, Universität Osnabrück, 49069 Osnabrück, and Max Planck Institut für Biophysik, Max-von-Laue-Strasse 3, 60438 Frankfurt/Main, Germany
| | - Jörg-Christian Greie
- Abteilung Mikrobiologie, Fachbereich Biologie/Chemie, Universität Osnabrück, 49069 Osnabrück, and Max Planck Institut für Biophysik, Max-von-Laue-Strasse 3, 60438 Frankfurt/Main, Germany
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13
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Three-dimensional structure of the KdpFABC complex of Escherichia coli by electron tomography of two-dimensional crystals. J Struct Biol 2007; 161:411-8. [PMID: 17945510 DOI: 10.1016/j.jsb.2007.09.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2007] [Revised: 08/13/2007] [Accepted: 09/11/2007] [Indexed: 11/23/2022]
Abstract
The KdpFABC complex (Kdp) functions as a K+ pump in Escherichia coli and is a member of the family of P-type ATPases. Unlike other family members, Kdp has a unique oligomeric composition and is notable for segregating K+ transport and ATP hydrolysis onto separate subunits (KdpA and KdpB, respectively). We have produced two-dimensional crystals of the KdpFABC complex within reconstituted lipid bilayers and determined its three-dimensional structure from negatively stained samples using a combination of electron tomography and real-space averaging. The resulting map is at a resolution of 2.4 nm and reveals a dimer of Kdp molecules as the asymmetric unit; however, only the cytoplasmic domains are visible due to the lack of stain penetration within the lipid bilayer. The sizes of these cytoplasmic domains are consistent with Kdp and, using a pseudo-atomic model, we have described the subunit interactions that stabilize the Kdp dimer within the larger crystallographic array. These results illustrate the utility of electron tomography in structure determination of ordered assemblies, especially when disorder is severe enough to hamper conventional crystallographic analysis.
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14
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Tholema N, Vor der Brüggen M, Mäser P, Nakamura T, Schroeder JI, Kobayashi H, Uozumi N, Bakker EP. All four putative selectivity filter glycine residues in KtrB are essential for high affinity and selective K+ uptake by the KtrAB system from Vibrio alginolyticus. J Biol Chem 2005; 280:41146-54. [PMID: 16210320 DOI: 10.1074/jbc.m507647200] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The subunit KtrB of bacterial Na+-dependent K+-translocating KtrAB systems belongs to a superfamily of K+ transporters. These proteins contain four repeated domains, each composed of two transmembrane helices connected by a putative pore loop (p-loop). The four p-loops harbor a conserved glycine residue at a position equivalent to a glycine selectivity filter residue in K+ channels. We investigated whether these glycines also form a selectivity filter in KtrB. The single residues Gly70, Gly185, Gly290, and Gly402 from p-loops P(A) to P(D) of Vibrio alginolyticus KtrB were replaced with alanine, serine, or aspartate. The three alanine variants KtrB(A70), KtrB(A185), and KtrB(A290) maintained a substantial activity in KtrAB-mediated K+ uptake in Escherichia coli. This activity was associated with a decrease in the affinity for K+ by 2 orders of magnitude, with little effect on Vmax. Minor activities were also observed for three other variants: KtrB(A402), KtrB(S70), and KtrB(D185). With all of these variants, the property of Na+ dependence of K+ transport was preserved. Only the four serine variants mediated Na+ uptake, and these variants differed considerably in their K+/Na+ selectivity. Experiments on cloned ktrB in the pBAD18 vector showed that V. alginolyticus KtrB alone was still active in E. coli. It mediated Na+-independent, slow, high affinity, and mutation-specific K+ uptake as well as K+-independent Na+ uptake. These data demonstrate that KtrB contains a selectivity filter for K+ ions and that all four conserved p-loop glycine residues are part of this filter. They also indicate that the role of KtrA lies in conferring velocity and ion coupling to the Ktr complex.
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Affiliation(s)
- Nancy Tholema
- Abteilung Mikrobiologie, Universität Osnabrück, D-49069 Osnabrück, Germany
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15
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Bramkamp M, Altendorf K. Single Amino Acid Substitution in the Putative Transmembrane Helix V in KdpB of the KdpFABC Complex of Escherichia coli Uncouples ATPase Activity and Ion Transport. Biochemistry 2005; 44:8260-6. [PMID: 15938615 DOI: 10.1021/bi050135n] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The KdpFABC complex, found in a variety of prokaryotes, is an emergency potassium uptake system which belongs to the family of P-type ATPases. Site-directed mutagenesis of the charged residues aspartate 583 and lysine 586 in the putative transmembrane helix V of subunit KdpB revealed that these charges are involved in the coupling of ATP hydrolysis and ion translocation. Phenotypic characterization of KdpFABC derivatives carrying alterations at either D583 or K586 demonstrated that only restoration of charges at these positions allowed growth on low potassium concentrations. Substitutions, which eliminated the negative charge at position 583, did not allow growth below 15 mM potassium on solid media. In contrast, substitutions of the positive charge at position 586 allowed growth down to 0.3 mM potassium. Purified KdpFABC complexes carrying these substitutions exhibited ATPase activity, which was, however, found to be comparatively resistant to o-vanadate. Furthermore, elimination of the charges led to a complete loss of ion-stimulated ATPase activity, though the rate of hydrolysis was comparable to wild-type activity, indicating an uncoupling between ATP hydrolysis and ion translocation. This fact was substantiated by reconstitution experiments, in which the D583A complex was unable to facilitate ion translocation, whereas the D583E mutant complex still exhibited such activity. On the basis of these results, a new transport model for the Kdp-ATPase is presented here, in which the amino acids D583 and K586 are supposed to play a role in the gating mechanism of the complex. Furthermore, movement of the charged side chains could have a direct influence on the free energy profile within the potassium transporting subunit KdpA, thereby facilitating ion transport against the concentration gradient into the cytosol.
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Affiliation(s)
- Marc Bramkamp
- Abteilung Mikrobiologie, Fachbereich Biologie/Chemie, Universität Osnabrück, D-49069 Osnabrück, Germany
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16
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Bertrand J, Altendorf K, Bramkamp M. Amino acid substitutions in putative selectivity filter regions III and IV in KdpA alter ion selectivity of the KdpFABC complex from Escherichia coli. J Bacteriol 2004; 186:5519-22. [PMID: 15292155 PMCID: PMC490938 DOI: 10.1128/jb.186.16.5519-5522.2004] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
When grown under conditions of potassium limitation or high osmolality, Escherichia coli synthesizes the K(+)-translocating KdpFABC complex. The KdpA subunit, which has sequence homology to potassium channels of the KcsA type, has been shown to be important for potassium binding and transport. Replacement of the glycine residues in KdpA at positions 345 and 470, members of putative selectivity filter regions III and IV, alters the ion selectivity of the KdpFABC complex.
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Affiliation(s)
- Jessica Bertrand
- Abteilung Mikrobiologie, Fachbereich Biologie/Chemie, Universität Osnabrück, D-49076 Osnabrueck, Germany
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17
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van der Laan M, Gassel M, Altendorf K. Characterization of amino acid substitutions in KdpA, the K+-binding and -translocating subunit of the KdpFABC complex of Escherichia coli. J Bacteriol 2002; 184:5491-4. [PMID: 12218037 PMCID: PMC135338 DOI: 10.1128/jb.184.19.5491-5494.2002] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
When grown under K+ limitation, Escherichia coli induces the K+-translocating KdpFABC complex. The stimulation of ATPase activity by NH4+ ions was shown for the first time. Substitutions in KdpA, which is responsible for K+ binding and translocation, revealed that enzyme complexes KdpA:G232A and KdpA:G232S have completely lost their cation selectivity.
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Affiliation(s)
- Martin van der Laan
- Abteilung Mikrobiologie, Fachbereich Biologie/Chemie, Universität Osnabrück, D-49069 Osnabrück, Germany
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Häse CC, Fedorova ND, Galperin MY, Dibrov PA. Sodium ion cycle in bacterial pathogens: evidence from cross-genome comparisons. Microbiol Mol Biol Rev 2001; 65:353-70, table of contents. [PMID: 11528000 PMCID: PMC99031 DOI: 10.1128/mmbr.65.3.353-370.2001] [Citation(s) in RCA: 189] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Analysis of the bacterial genome sequences shows that many human and animal pathogens encode primary membrane Na+ pumps, Na+-transporting dicarboxylate decarboxylases or Na+ translocating NADH:ubiquinone oxidoreductase, and a number of Na+ -dependent permeases. This indicates that these bacteria can utilize Na+ as a coupling ion instead of or in addition to the H+ cycle. This capability to use a Na+ cycle might be an important virulence factor for such pathogens as Vibrio cholerae, Neisseria meningitidis, Salmonella enterica serovar Typhi, and Yersinia pestis. In Treponema pallidum, Chlamydia trachomatis, and Chlamydia pneumoniae, the Na+ gradient may well be the only energy source for secondary transport. A survey of preliminary genome sequences of Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans, and Treponema denticola indicates that these oral pathogens also rely on the Na+ cycle for at least part of their energy metabolism. The possible roles of the Na+ cycling in the energy metabolism and pathogenicity of these organisms are reviewed. The recent discovery of an effective natural antibiotic, korormicin, targeted against the Na+ -translocating NADH:ubiquinone oxidoreductase, suggests a potential use of Na+ pumps as drug targets and/or vaccine candidates. The antimicrobial potential of other inhibitors of the Na+ cycle, such as monensin, Li+ and Ag+ ions, and amiloride derivatives, is discussed.
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Affiliation(s)
- C C Häse
- Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA
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Dorus S, Mimura H, Epstein W. Substrate-binding clusters of the K+-transporting Kdp ATPase of Escherichia coli investigated by amber suppression scanning mutagenesis. J Biol Chem 2001; 276:9590-8. [PMID: 11106663 DOI: 10.1074/jbc.m009365200] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Kdp-ATPase of Escherichia coli is a four-subunit P-type ATPase that accumulates K(+) with high affinity and specificity. Residues clustered in four regions of the KdpA subunit of Kdp were implicated as critical for K(+) binding from the analysis of mutants with reduced affinity for K(+) (Buurman, E., Kim, K.-T., and Epstein, W. (1995) J. Biol. Chem. 270, 6678-6685). K(+) binding by this pump has been analyzed in detail by site-directed mutagenesis. We have examined 83 of the 557 residues in KdpA, from 11 to 34 residues in each of four binding clusters known to affect K(+) binding. Amber mutations were constructed in a plasmid carrying the kdpFABC structural genes. Transferring these plasmids to 12 suppressor strains, each inserting a different amino acid at amber codons, created 12 different substitutions at the mutated sites. This study delineates the four clusters and confirms that they are important for K(+) affinity but have little effect on the rate of transport. At only 21 of the residues studied did at least three substitutions alter affinity for K(+), an indication that a residue is in or very near a K(+) binding site. At many residues lysine was the only substitution that altered its affinity. The effect of lysine is most likely a repulsive effect of this cationic residue on K(+) and thus reflects the effective distance between a residue and the site of binding or passage of K(+) in KdpA. Once a crystallographic structure of Kdp is available, this measure of effective distance will help identify the path of K(+) as it moves through the KdpA subunit to cross the membrane.
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Affiliation(s)
- S Dorus
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Illinois 60637, USA
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