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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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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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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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Sato Y, Nanatani K, Hamamoto S, Shimizu M, Takahashi M, Tabuchi-Kobayashi M, Mizutani A, Schroeder JI, Souma S, Uozumi N. Defining membrane spanning domains and crucial membrane-localized acidic amino acid residues for K+ transport of a Kup/HAK/KT-type Escherichia coli potassium transporter. ACTA ACUST UNITED AC 2014; 155:315-23. [DOI: 10.1093/jb/mvu007] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
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Kogenaru S, Qing Y, Guo Y, Wang N. RNA-seq and microarray complement each other in transcriptome profiling. BMC Genomics 2012; 13:629. [PMID: 23153100 PMCID: PMC3534599 DOI: 10.1186/1471-2164-13-629] [Citation(s) in RCA: 106] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2012] [Accepted: 11/05/2012] [Indexed: 12/22/2022] Open
Abstract
Background RNA-seq and microarray are the two popular methods employed for genome-wide transcriptome profiling. Current comparison studies have shown that transcriptome quantified by these two methods correlated well. However, none of them have addressed if they complement each other, considering the strengths and the limitations inherent with them. The pivotal requirement to address this question is the knowledge of a well known data set. In this regard, HrpX regulome from pathogenic bacteria serves as an ideal choice as the target genes of HrpX transcription factor are well studied due to their central role in pathogenicity. Results We compared the performance of RNA-seq and microarray in their ability to detect known HrpX target genes by profiling the transcriptome from the wild-type and the hrpX mutant strains of γ-Proteobacterium Xanthomonas citri subsp. citri. Our comparative analysis indicated that gene expression levels quantified by RNA-seq and microarray well-correlated both at absolute as well as relative levels (Spearman correlation-coefficient, rs > 0.76). Further, the expression levels quantified by RNA-seq and microarray for the significantly differentially expressed genes (DEGs) also well-correlated with qRT-PCR based quantification (rs = 0.58 to 0.94). Finally, in addition to the 55 newly identified DEGs, 72% of the already known HrpX target genes were detected by both RNA-seq and microarray, while, the remaining 28% could only be detected by either one of the methods. Conclusions This study has significantly advanced our understanding of the regulome of the critical transcriptional factor HrpX. RNA-seq and microarray together provide a more comprehensive picture of HrpX regulome by uniquely identifying new DEGs. Our study demonstrated that RNA-seq and microarray complement each other in transcriptome profiling.
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Affiliation(s)
- Sunitha Kogenaru
- Citrus Research and Education Center, Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, 700 Experiment Station Road, Lake Alfred, FL 33850, USA
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Glaves JP, Fisher L, Ward A, Young HS. Helical crystallization of two example membrane proteins MsbA and the Ca(2+)-ATPase. Methods Enzymol 2010; 483:143-59. [PMID: 20888473 DOI: 10.1016/s0076-6879(10)83007-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Helical crystallization is a powerful tool for the moderate resolution structure determination of integral membrane proteins, where the insight gained often includes domain architecture and the disposition of α-helical segments. A necessary first step toward helical crystallization involves membrane protein reconstitution, which itself is a powerful technique for structure-function studies of integral membrane proteins. The correct insertion of a detergent-solubilized, purified membrane protein into lipid vesicles (proteoliposomes) can facilitate the functional characterization of the protein in a well-defined, chemically pure environment without interference from other membrane-associated components. In addition, the lipid-to-protein ratio can be controlled during reconstitution to generate a high concentration of a particular membrane protein in the proteoliposomes, which are then suitable for both functional assays and crystallization trials. Traditional approaches to two-dimensional crystallization for electron microscopy rely on dialysis methods for the simultaneous reconstitution and crystallization of a membrane protein [Kühlbrandt, W. (1992). Two-dimensional crystallization of membrane proteins. Q. Rev. Biophys.25, 1-49.], yet some systems allow these two steps to be experimentally separated and independently considered. Some examples of integral membrane proteins that have been reconstituted and crystallized in a helical lattice include cytochrome bc1 complex from bovine heart [Akiba, T., et al. (1996). Three-dimensional structure of bovine cytochrome bc(1) complex by electron cryomicroscopy and helical image reconstruction. Nat. Struct. Biol.3, 553-561.], Escherichia coli melibiose permease [Rigaud, J. L., et al. (1997). Bio-beads: An efficient strategy for two-dimensional crystallization of membrane proteins. J. Struct. Biol.118, 226-235.], a bacterial ATP-binding cassette transporter MsbA [Ward, A., et al. (2009). Nucleotide dependent packing differences in helical crystals of the ABC transporter MsbA. J. Struct. Biol.165, 169-175.], and the sarcoplasmic reticulum Ca(2+)-ATPase [Young, H. S., et al. (1997). How to make tubular crystals by reconstitution of detergent-solubilized Ca(2+)-ATPase. Biophys. J.72, 2545-2558.]. The reconstitution and helical crystallization of MsbA and Ca(2+)-ATPase will be the focus of this chapter.
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Affiliation(s)
- John Paul Glaves
- Department of Biochemistry, School of Molecular and Systems Medicine, University of Alberta, Edmonton, Alberta, Canada
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