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Plotkin BJ, Halkyard S, Spoolstra E, Micklo A, Kaminski A, Sigar IM, Konaklieva MI. The Role of the Insulin/Glucose Ratio in the Regulation of Pathogen Biofilm Formation. BIOLOGY 2023; 12:1432. [PMID: 37998031 PMCID: PMC10669081 DOI: 10.3390/biology12111432] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2023] [Revised: 11/07/2023] [Accepted: 11/09/2023] [Indexed: 11/25/2023]
Abstract
During the management of patients in acute trauma the resulting transient hyperglycemia is treated by administration of insulin. Since the effect of insulin, a quorum sensing compound, together with glucose affects biofilm formation in a concentration-specific manner, we hypothesize that the insulin/glucose ratio over the physiologic range modulates biofilm formation potentially influencing the establishment of infection through biofilm formation. METHODS A variety of Gram-positive and Gram-negative bacteria were grown in peptone (1%) yeast nitrogen base broth overnight in 96-well plates with various concentrations of glucose and insulin. Biofilm formation was determined by the crystal violet staining procedure. Expression of insulin binding was determined by fluorescent microscopy (FITC-insulin). Controls were buffer alone, insulin alone, and glucose alone. RESULTS Overall, maximal biofilm levels were measured at 220 mg/dL of glucose, regardless of insulin concentration (10, 100, 200 µU/mL) of the organism tested. In general, insulin with glucose over the range of 160-180 mg/dL exhibited a pattern of biofilm suppression. However, either above or below this range, the presence of insulin in combination with glucose significantly modulated (increase or decrease) biofilm formation in a microbe-specific pattern. This modulation appears for some organisms to be reflective of the glucose-regulated intrinsic expression of bacterial insulin receptor expression. CONCLUSION Insulin at physiologic levels (normal and hyperinsulinemic) in combination with glucose can affect biofilm formation in a concentration-specific and microbe-specific manner. These findings may provide insight into the importance of co-regulation of the insulin/glucose ratio in patient management.
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Affiliation(s)
- Balbina J. Plotkin
- Department of Microbiology and Immunology, Midwestern University, Downers Grove, IL 60515, USA; (S.H.); (E.S.); (A.M.); (A.K.); (I.M.S.)
| | - Scott Halkyard
- Department of Microbiology and Immunology, Midwestern University, Downers Grove, IL 60515, USA; (S.H.); (E.S.); (A.M.); (A.K.); (I.M.S.)
| | - Emily Spoolstra
- Department of Microbiology and Immunology, Midwestern University, Downers Grove, IL 60515, USA; (S.H.); (E.S.); (A.M.); (A.K.); (I.M.S.)
| | - Amanda Micklo
- Department of Microbiology and Immunology, Midwestern University, Downers Grove, IL 60515, USA; (S.H.); (E.S.); (A.M.); (A.K.); (I.M.S.)
| | - Amber Kaminski
- Department of Microbiology and Immunology, Midwestern University, Downers Grove, IL 60515, USA; (S.H.); (E.S.); (A.M.); (A.K.); (I.M.S.)
| | - Ira M. Sigar
- Department of Microbiology and Immunology, Midwestern University, Downers Grove, IL 60515, USA; (S.H.); (E.S.); (A.M.); (A.K.); (I.M.S.)
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Nan B, Liu X, Zhou Y, Liu J, Zhang L, Wen J, Zhang X, Su XD, Wang YP. From signal perception to signal transduction: ligand-induced dimeric switch of DctB sensory domain in solution. Mol Microbiol 2010; 75:1484-94. [PMID: 20149110 DOI: 10.1111/j.1365-2958.2010.07069.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Sinorhizobium meliloti DctB is a typical transmembrane sensory histidine kinase, which senses C(4)-dicarboxylic acids (DCA) and regulates the expression of DctA, the DCA transporter. We previously reported the crystal structures of its periplasmic sensory domain (DctBp) in apo and succinate-bound states, and these structures showed dramatic conformational changes at dimeric level. Here we show a ligand-induced dimeric switch in solution and a strong correlation between DctBp's dimerization states and the in vivo activities of DctB. Using site-directed mutagenesis, we identify important determinants for signal perception and transduction. Specifically, we show that the ligand-binding pocket is essential for DCA-induced 'on' activity of DctB. Mutations at different sections of DctBp's dimerization interface can lock full-length DctB at either 'on' or 'off' state, independent of ligand binding. Taken together, these results suggest that DctBp's signal perception and transduction occur through a 'ligand-induced dimeric switch', in which the changes in the dimeric conformations upon ligand binding are responsible for the signal transduction in DctB.
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Affiliation(s)
- Beiyan Nan
- National Laboratory of Protein Engineering and Plant Genetic Engineering, College of Life Sciences, Peking University, Beijing, China
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3
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Ward SM, Bormans AF, Manson MD. Mutationally altered signal output in the Nart (NarX-Tar) hybrid chemoreceptor. J Bacteriol 2006; 188:3944-51. [PMID: 16707686 PMCID: PMC1482925 DOI: 10.1128/jb.00117-06] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Signal-transducing proteins that span the cytoplasmic membrane transmit information about the environment to the interior of the cell. In bacteria, these signal transducers include sensor kinases, which typically control gene expression via response regulators, and methyl-accepting chemoreceptor proteins, which control flagellar rotation via the CheA kinase and CheY response regulator. We previously reported that a chimeric protein (Nart) that joins the ligand-binding, transmembrane, and linker regions of the NarX sensor kinase to the signaling and adaptation domains of the Tar chemoreceptor elicits a repellent response to nitrate and nitrite. As with NarX, nitrate evokes a stronger response than nitrite. Here we show that mutations targeting a highly conserved sequence (the P box) in the periplasmic domain alter chemoreception by Nart and signaling by NarX similarly. In particular, the G51R substitution converts Nart from a repellent receptor into an attractant receptor for nitrate. Our results underscore the conclusion that the fundamental mechanism of transmembrane signaling is conserved between homodimeric sensor kinases and chemoreceptors. They also highlight the plasticity of the coupling between ligand binding and signal output in these systems.
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Affiliation(s)
- Scott M Ward
- Department of Biology, 3258 TAMU, Texas A&M University, College Station, TX 77843, USA
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4
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Abstract
The PAS and HAMP domain superfamilies are signal transduction modules found in all kingdoms of life. The Aer receptor, which contains both domains, initiates rapid behavioural responses to oxygen (aerotaxis) and other electron acceptors, guiding Escherichia coli to niches where it can generate optimal cellular energy. We used intragenic complementation to investigate the signal transduction pathway from the Aer PAS domain to the signalling domain. These studies showed that the HAMP domain of one monomer in the Aer dimer stabilized FAD binding to the PAS domain of the cognate monomer. In contrast, the signal transduction pathway was intra-subunit, involving the PAS and signalling domains from the same monomer. The minimal requirements for signalling were investigated in heterodimers containing a full-length and truncated monomer. Either the PAS or signalling domains could be deleted from the non-signalling subunit of the heterodimer, but removing 16 residues from the C-terminus of the signalling subunit abolished aerotaxis. Although both HAMP domains were required for aerotaxis, signalling was not disrupted by missense mutations in the HAMP domain from the signalling subunit. Possible models for Aer signal transduction are compared.
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Affiliation(s)
- Kylie J Watts
- Division of Microbiology and Molecular Genetics, Loma Linda University, Loma Linda, CA 92350, USA
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5
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Kiessling LL, Gestwicki JE, Strong LE. Synthetische multivalente Liganden als Sonden für die Signaltransduktion. Angew Chem Int Ed Engl 2006. [DOI: 10.1002/ange.200502794] [Citation(s) in RCA: 122] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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6
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Kiessling LL, Gestwicki JE, Strong LE. Synthetic multivalent ligands as probes of signal transduction. Angew Chem Int Ed Engl 2006; 45:2348-68. [PMID: 16557636 PMCID: PMC2842921 DOI: 10.1002/anie.200502794] [Citation(s) in RCA: 687] [Impact Index Per Article: 38.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Cell-surface receptors acquire information from the extracellular environment and coordinate intracellular responses. Many receptors do not operate as individual entities, but rather as part of dimeric or oligomeric complexes. Coupling the functions of multiple receptors may endow signaling pathways with the sensitivity and malleability required to govern cellular responses. Moreover, multireceptor signaling complexes may provide a means of spatially segregating otherwise degenerate signaling cascades. Understanding the mechanisms, extent, and consequences of receptor co-localization and interreceptor communication is critical; chemical synthesis can provide compounds to address the role of receptor assembly in signal transduction. Multivalent ligands can be generated that possess a variety of sizes, shapes, valencies, orientations, and densities of binding elements. This Review focuses on the use of synthetic multivalent ligands to characterize receptor function.
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Affiliation(s)
- Laura L Kiessling
- Department of Chemistry, University of Wisconsin--Madison, 1101 University Ave., Madison, WI 53706, USA.
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7
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Winston SE, Mehan R, Falke JJ. Evidence that the adaptation region of the aspartate receptor is a dynamic four-helix bundle: cysteine and disulfide scanning studies. Biochemistry 2005; 44:12655-66. [PMID: 16171380 PMCID: PMC2902788 DOI: 10.1021/bi0507884] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The aspartate receptor is one of the ligand-specific, homodimeric chemoreceptors that detects extracellular attractants and triggers the chemotaxis pathway of Escherichia coli and Salmonella typhimurium. This receptor regulates the activity of the histidine kinase CheA, which forms a kinetically stable complex with the receptor cytoplasmic domain. An atomic four-helix bundle model has been constructed for this domain, which is functionally subdivided into the signaling and adaptation subdomains. The proposed four-helix bundle structure of the signaling subdomain, which binds CheA, is fully supported by experimental evidence. Much less evidence is available to test the four-helix bundle model of the adaptation subdomain, which possesses covalent adaptation sites and docking surfaces for adaptation enzymes. The present study focuses on a putative helix near the C terminus of the adaptation subdomain. To probe the structural and functional features of positions G467-A494 in this C-terminal region, a cysteine and disulfide scanning approach has been employed. Measurement of the chemical reactivities of scanned cysteines reveals an alpha-helical periodicity of exposed and buried residues, confirming alpha-helical secondary structure and mapping out a buried packing face. The effects of cysteine substitutions on activity in vivo and in vitro highlight the functional importance of the helix, especially its buried face. A scan for disulfide bond formation between symmetric pairs of engineered cysteines reveals promiscuous collisions between subunits, indicating the presence of significant thermal dynamics. A scan for functional disulfides reveals lock-on and signal-retaining disulfide bonds formed between symmetric pairs of cysteines at buried positions, indicating that the buried face of the helix lies near the subunit interface of the homodimer in the equilibrium structures of both the apo and aspartate-bound states where it plays a critical role in kinase regulation. These results strongly support the existing four-helix bundle model of the adaptation subdomain structure. A mechanistic model is proposed in which a signal is transmitted through the adaptation subdomain by a change in supercoiling of the four-helix bundle.
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Affiliation(s)
| | | | - Joseph J. Falke
- To whom correspondence should be addressed. Telephone: 303-492-3503. Fax: 303-492-5894.
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8
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Abstract
Motile bacteria respond to environmental cues to move to more favorable locations. The components of the chemotaxis signal transduction systems that mediate these responses are highly conserved among prokaryotes including both eubacterial and archael species. The best-studied system is that found in Escherichia coli. Attractant and repellant chemicals are sensed through their interactions with transmembrane chemoreceptor proteins that are localized in multimeric assemblies at one or both cell poles together with a histidine protein kinase, CheA, an SH3-like adaptor protein, CheW, and a phosphoprotein phosphatase, CheZ. These multimeric protein assemblies act to control the level of phosphorylation of a response regulator, CheY, which dictates flagellar motion. Bacterial chemotaxis is one of the most-understood signal transduction systems, and many biochemical and structural details of this system have been elucidated. This is an exciting field of study because the depth of knowledge now allows the detailed molecular mechanisms of transmembrane signaling and signal processing to be investigated.
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Affiliation(s)
- Melinda D Baker
- Department of Chemistry, Princeton University, Princeton, NJ 08544, USA
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9
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Zhu Y, Inouye M. The HAMP linker in histidine kinase dimeric receptors is critical for symmetric transmembrane signal transduction. J Biol Chem 2004; 279:48152-8. [PMID: 15316026 DOI: 10.1074/jbc.m401024200] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The HAMP linker, a common structural element between a sensor and a transmitter module in various sensor proteins, plays an essential role in signal transduction. Here, by in vivo complementation experiments with Tar-EnvZ hybrid receptor mutants in which the HAMP linker forms a heterodimer with Tar and EnvZ-type subunits, we found that mutations at one linker only affect the function of EnvZ in the same subunit. However, the same mutations affect the EnvZ function of both subunits when only a Tar or EnvZ-type HAMP linker is used. These results suggest that intersubunit interactions in the HAMP linker normally mediate signal transduction through both subunits in a sensor dimer, whereas the signal is asymmetrically transduced through the linker in a heterodimer. This is the first demonstration that two HAMP linkers in a sensor dimer are functionally coupled for normal signal transduction; however, this functional coupling can be reduced when the HAMP linkers lose their symmetric nature.
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Affiliation(s)
- Yan Zhu
- Department of Biochemistry, Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA
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10
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Shiomi D, Homma M, Kawagishi I. Intragenic suppressors of a mutation in the aspartate chemoreceptor gene that abolishes binding of the receptor to methyltransferase. MICROBIOLOGY (READING, ENGLAND) 2002; 148:3265-3275. [PMID: 12368460 DOI: 10.1099/00221287-148-10-3265] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
In the chemotaxis of Escherichia coli, receptor methylation is the key process of adaptation. The methyltransferase CheR binds to the carboxy-terminal NWETF sequence of major chemoreceptors. The substitution of Ala for Trp of this sequence (W550A) of the aspartate chemoreceptor (Tar) abolishes its CheR-binding ability. In this study, six independent intragenic suppressors of the mutation were isolated. They were divided into two classes. Tar carrying the class I suppressors (G278A-L488M, T334A, G278A, G278C and A398T) showed signal biases toward tumbling, corresponding to increased activities of the receptor-associated histidine kinase CheA. These suppressors further reduced the unstimulated methylation level of Tar-W550A, but allowed slight but significant stimulation of methylation by aspartate. Some other CheA-activating mutations were also found to serve as class I suppressors. These results suggest that the class I suppressors compensate for the signal bias of Tar-W550A caused by its low methylation level and that the NWETF sequence is required primarily to maintain an appropriate level of methylation by increasing the local concentration of CheR around the receptor. The class II suppressor was a mutation in the termination codon (Op554W) resulting in the addition of 11 residues containing an xWxxF motif. This revertant Tar supported chemotaxis and was methylated almost as effectively as wild-type Tar. This effect was reversed by introducing a mutation in the xWxxF motif. These results reinforce the importance of the xWxxF motif and suggest that the motif does not have to be located at the extreme carboxy terminus.
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Affiliation(s)
- Daisuke Shiomi
- Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan1
| | - Michio Homma
- Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan1
| | - Ikuro Kawagishi
- Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan1
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11
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Abstract
Chemotaxis transducers are specialized receptors that microorganisms use in order to sense the environment in directing their motility to favorable niches. The Escherichia coli transducers are models for studying the sensory and signaling events at the molecular level. Extensive studies in other organisms and the arrival of genomics has resulted in the accumulation of sequences of many transducer genes, but they are not fully understood. In silico analysis provides some assistance in classification of various transducers from different species and in predicting their function. All transducers contain two structural modules: a conserved C-terminal multidomain module, which is a signature element of the transducer superfamily, and a variable N-terminal module, which is responsible for the diversity within the superfamily. These structural modules have two distinct functions: the conserved C-terminal module is involved in signaling and adaptation, and the N-terminal module is involved in sensing various stimuli. Both C-terminal and N-terminal modules appear to be mobile genetic elements and subjects of duplication and lateral transfer. Although chemotaxis transducers are found exclusively in prokaryotic organisms that have some type of motility (flagellar, gliding or pili-based), several types of domains that are found in their N-terminal modules are also present in signal transduction proteins from eukaryotes, including humans. This indicates that basic principles of sensory transduction are conserved throughout the phylogenetic tree and that the chemotaxis transducer superfamily is a valuable source of novel sensory elements yet to be discovered.
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Affiliation(s)
- I B Zhulin
- School of Biology, Georgia Institute of Technology, 310 Ferst Drive, Atlanta, GA 30332-0230, USA.
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12
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Gestwicki JE, Kiessling LL. Inter-receptor communication through arrays of bacterial chemoreceptors. Nature 2002; 415:81-4. [PMID: 11780121 DOI: 10.1038/415081a] [Citation(s) in RCA: 221] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The sensing mechanisms of chemotactic bacteria allow them to respond sensitively to stimuli. Escherichia coli, for example, respond to changes in chemoattractant concentration of less than 10% over a range spanning six orders of magnitude. Sensitivity over this range depends on a nonlinear relationship between ligand concentration and output response. At low ligand concentrations, substantial amplification of the chemotactic signal is required; however, the mechanism responsible for this amplification remains unclear. Here we demonstrate that inter-receptor communication within a lattice acts to amplify and integrate sensory information. Synthetic multivalent ligands that interact through the low-abundance, galactose-sensing receptor Trg stabilize large clusters of chemoreceptors and markedly enhance signal output from these enforced clusters. On treatment with multivalent ligands, the response to the attractant serine is amplified by at least 100-fold. This amplification requires a full complement of chemoreceptors; deletion of the aspartate (Tar) or dipeptide (Tap) receptors diminishes the amplification of the serine response. These results demonstrate that the entire array is involved in sensing. This mode of information exchange has general implications for the processing of signals by cellular receptors.
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Affiliation(s)
- Jason E Gestwicki
- Department of Chemistry, University of Wisconsin-Madison, 53706, USA
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13
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Murphy OJ, Yi X, Weis RM, Thompson LK. Hydrogen exchange reveals a stable and expandable core within the aspartate receptor cytoplasmic domain. J Biol Chem 2001; 276:43262-9. [PMID: 11553619 DOI: 10.1074/jbc.m105585200] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Intensive study of bacterial chemoreceptors has not yet revealed how receptor methylation and ligand binding alter the interactions between the receptor cytoplasmic domain and the CheA kinase to control kinase activity. Both monomeric and dimeric forms of an Asp receptor cytoplasmic fragment have been shown to be highly dynamic, with a small core of slowly exchanging amide hydrogens (Seeley, S. K., Weis, R. M., and Thompson, L. K. (1996) Biochemistry 35, 5199-5206). Hydrogen exchange studies of the wild-type cytoplasmic fragment and an S461L mutant thought to mimic the kinase-inactivating state are used to investigate the relationship between the stable core and dimer dissociation. Our results establish that (i) decreasing pH stabilizes the dimeric state, (ii) the stable core is present also in the transition state for dissociation, and (iii) this core is expanded significantly by small changes in electrostatic and hydrophobic interactions. These kinase-inactivating changes stabilize both the monomeric and the dimeric states of the protein, which has interesting implications for the mechanism of kinase activation. We conclude that the cytoplasmic domain is a flexible region poised for stabilization by small changes in electrostatic and hydrophobic interactions such as those caused by methylation of glutamate residues and by ligand-induced conformational changes during signaling.
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Affiliation(s)
- O J Murphy
- Graduate Program in Molecular and Cellular Biology, and the Department of Chemistry, University of Massachusetts, Amherst, Massachusetts 01003-4510, USA
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14
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Jung KH, Spudich EN, Trivedi VD, Spudich JL. An archaeal photosignal-transducing module mediates phototaxis in Escherichia coli. J Bacteriol 2001; 183:6365-71. [PMID: 11591681 PMCID: PMC100132 DOI: 10.1128/jb.183.21.6365-6371.2001] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Halophilic archaea, such as Halobacterium salinarum and Natronobacterium pharaonis, alter their swimming behavior by phototaxis responses to changes in light intensity and color using visual pigment-like sensory rhodopsins (SRs). In N. pharaonis, SRII (NpSRII) mediates photorepellent responses through its transducer protein, NpHtrII. Here we report the expression of fusions of NpSRII and NpHtrII and fusion hybrids with eubacterial cytoplasmic domains and analyze their function in vivo in haloarchaea and in eubacteria. A fusion in which the C terminus of NpSRII is connected by a short flexible linker to NpHtrII is active in phototaxis signaling for H. salinarum, showing that the fusion does not inhibit functional receptor-transducer interactions. We replaced the cytoplasmic portions of this fusion protein with the cytoplasmic domains of Tar and Tsr, chemotaxis transducers from enteric eubacteria. Purification of the fusion protein from H. salinarum and Tar fusion chimera from Escherichia coli membranes shows that the proteins are not cleaved and exhibit absorption spectra characteristic of wild-type membranes. Their photochemical reaction cycles in H. salinarum and E. coli membranes, respectively, are similar to those of native NpSRII in N. pharaonis. These fusion chimeras mediate retinal-dependent phototaxis responses by Escherichia coli, establishing that the nine-helix membrane portion of the receptor-transducer complex is a modular functional unit able to signal in heterologous membranes. This result confirms a current model for SR-Htr signal transduction in which the Htr transducers are proposed to interact physically and functionally with their cognate sensory rhodopsins via helix-helix contacts between their transmembrane segments.
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Affiliation(s)
- K H Jung
- Department of Microbiology and Molecular Genetics, University of Texas-Houston Medical School, Houston, Texas 77030, USA
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15
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Affiliation(s)
- H Saito
- Dana-Farber Cancer Institute, and Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 44 Binney Street, Boston, Massachusetts 02115, USA.
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16
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Shi Y. Effects of thermal fluctuation and the receptor-receptor interaction in bacterial chemotactic signaling and adaptation. PHYSICAL REVIEW E 2001; 64:021910. [PMID: 11497623 DOI: 10.1103/physreve.64.021910] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2000] [Indexed: 11/07/2022]
Abstract
Bacterial chemotaxis is controlled by the conformational changes of the receptors in response to the change of the ambient chemical concentration. In a statistical mechanical approach, the signaling due to the conformational changes is a thermodynamic average quantity, dependent on the temperature and the total energy of the system, including both ligand-receptor interaction and receptor-receptor interaction. This physical theory suggests to biology an understanding of cooperation in ligand binding and receptor signaling problems. How much experimental support of this approach can be obtained from the currently available data? What are the parameter values? What is the practical information for experiments? Here we make comparisons between the theory and recent experimental results. Although currently comparisons can only be semiquantitative or qualitative, consistency is clearly shown. The theory also helps to sort a variety of data.
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Affiliation(s)
- Y Shi
- Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom.
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17
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Beel BD, Hazelbauer GL. Signalling substitutions in the periplasmic domain of chemoreceptor Trg induce or reduce helical sliding in the transmembrane domain. Mol Microbiol 2001; 40:824-34. [PMID: 11401690 DOI: 10.1046/j.1365-2958.2001.02446.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We used in vivo oxidative cross-linking of engineered cysteine pairs to assess conformational changes in the four-helix transmembrane domain of chemoreceptor Trg. Extending previous work, we searched for and found a fourth cross-linking pair that spanned the intrasubunit interface between transmembrane helix 1 (TM1) and its partner TM2. We determined the effects of ligand occupancy on cross-linking rate constants for all four TM1-TM2 diagnostic pairs in conditions that allowed the formation of receptor-kinase complexes for the entire cellular complement of Trg. Occupancy altered all four rates in a pattern that implicated sliding of TM2 relative to TM1 towards the cytoplasm as the transmembrane signalling movement in receptor-kinase complexes. Transmembrane signalling can be reduced or induced by single amino acid substitutions in the ligand-binding region of the periplasmic domain of Trg. We determined the effects of these substitutions on conformation in the transmembrane domain and on ligand-induced changes using the diagnostic TM1-TM2 cysteine pairs. Effects on rates of in vivo cross-linking showed that induced signalling substitutions altered the relative positions of TM1 and TM2 in the same way as ligand binding, and reduced signalling substitutions blocked or attenuated the ligand-induced shift. These results provide strong support for the helical sliding model of transmembrane signalling.
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Affiliation(s)
- B D Beel
- School of Molecular Biosciences, Washington State University, Pullman, WA 99164-4660, USA
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18
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Abstract
Bacterial chemoreceptors mediate chemotaxis by recognizing specific chemicals and regulating a noncovalently associated histidine kinase. Ligand binding to the external domain of the membrane-spanning receptor generates a transmembrane signal that modulates kinase activity inside the cell. This transmembrane signaling is being investigated by novel strategies, which have revealed a remarkably subtle conformational signal carried by a signaling helix that spans the entire length of the >350-A-long receptor. Multiple, independent lines of evidence indicate that, in the periplasmic and transmembrane domains, conformational signaling is a piston-type sliding of the signaling helix towards the cytoplasm.
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Affiliation(s)
- Joseph J. Falke
- Dept of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309-0215, USA.
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19
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Bren A, Eisenbach M. How signals are heard during bacterial chemotaxis: protein-protein interactions in sensory signal propagation. J Bacteriol 2000; 182:6865-73. [PMID: 11092844 PMCID: PMC94809 DOI: 10.1128/jb.182.24.6865-6873.2000] [Citation(s) in RCA: 262] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Affiliation(s)
- A Bren
- Department of Biological Chemistry, The Weizmann Institute of Science, 76100 Rehovot, Israel
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20
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Gestwicki JE, Lamanna AC, Harshey RM, McCarter LL, Kiessling LL, Adler J. Evolutionary conservation of methyl-accepting chemotaxis protein location in Bacteria and Archaea. J Bacteriol 2000; 182:6499-502. [PMID: 11053396 PMCID: PMC94798 DOI: 10.1128/jb.182.22.6499-6502.2000] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The methyl-accepting chemotaxis proteins (MCPs) are concentrated at the cell poles in an evolutionarily diverse panel of bacteria and an archeon. In elongated cells, the MCPs are located both at the poles and at regions along the length of the cells. Together, these results suggest that MCP location is evolutionarily conserved.
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Affiliation(s)
- J E Gestwicki
- Departments of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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21
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Bornhorst JA, Falke JJ. Attractant regulation of the aspartate receptor-kinase complex: limited cooperative interactions between receptors and effects of the receptor modification state. Biochemistry 2000; 39:9486-93. [PMID: 10924144 PMCID: PMC2890267 DOI: 10.1021/bi0002737] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The manner by which the bacterial chemotaxis system responds to a wide range of attractant concentrations remains incompletely understood. In principle, positive cooperativity between chemotaxis receptors could explain the ability of bacteria to respond to extremely low attractant concentrations. By utilizing an in vitro receptor-coupled kinase assay, the attractant-dependent response curve has been measured for the Salmonella typhimurium aspartate chemoreceptor. The attractant chosen, alpha-methyl aspartate, was originally used to quantitate high receptor sensitivity at low attractant concentrations by Segall, Block, and Berg [(1986) Proc. Natl. Acad. Sci. U.S.A. 83, 8987-8991]. The attractant response curve exhibits limited positive cooperativity, yielding a Hill coefficient of 1.7-2.4, and this Hill coefficient is relatively independent of both the receptor modification state and the mole ratio of CheA to receptor. These results disfavor models in which there are strong cooperative interactions between large numbers of receptor dimers in an extensive receptor array. Instead, the results are consistent with cooperative interactions between a small number of coupled receptor dimers. Because the in vitro receptor-coupled kinase assay utilizes higher than native receptor densities arising from overexpression, the observed positive cooperativity may overestimate that present in native receptor populations. Such positive cooperativity between dimers is fully compatible with the negative cooperativity previously observed between the two symmetric ligand binding sites within a single dimer. The attractant affinity of the aspartate receptor is found to depend on the modification state of its covalent adaptation sites. Increasing the the level of modification decreases the apparent attractant affinity at least 10-fold in the in vitro receptor-coupled kinase assay. This observation helps explain the ability of the chemotaxis pathway to respond to a broad range of attractant concentrations in vivo.
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Affiliation(s)
| | - Joseph J. Falke
- Corresponding author. Telephone: (303) 492-3503. Fax: (303) 492-5894.
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22
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Falke JJ, Kim SH. Structure of a conserved receptor domain that regulates kinase activity: the cytoplasmic domain of bacterial taxis receptors. Curr Opin Struct Biol 2000; 10:462-9. [PMID: 10981636 PMCID: PMC2902786 DOI: 10.1016/s0959-440x(00)00115-9] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Many bacteria are motile and use a conserved class of transmembrane sensory receptor to regulate cellular taxis toward an optimal living environment. These conserved receptors are typically stimulated by extracellular signals, but also undergo adaptation via covalent modification at specific sites on their cytoplasmic domains. The function of the cytoplasmic domain is to integrate the extracellular and adaptive signals, and to use this integrated information to regulate an associated histidine kinase. The kinase, in turn, triggers a cytoplasmic phosphorylation pathway of the two-component class. The high-resolution structure of a receptor cytoplasmic domain has recently been determined by crystallographic methods and is largely consistent with a structural model independently generated by chemical studies of the domain in the full-length, membrane-bound receptor. These results represent an important step toward a mechanistic understanding of receptor-to-kinase information transfer.
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Affiliation(s)
- Joseph J Falke
- Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, USA
| | - Sung-Hou Kim
- Department of Chemistry and Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720-5230, USA
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23
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Manson MD. Allele-specific suppression as a tool to study protein-protein interactions in bacteria. Methods 2000; 20:18-34. [PMID: 10610801 DOI: 10.1006/meth.1999.0902] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Suppression analysis is well suited to study the interactions of gene products. It offers the advantage of simplicity for any organism for which a convenient genetic system has been developed, which holds for a wide spectrum of bacteria and an ever-increasing number of unicellular as well as complex eukaryotes. No other method provides as much information about the functional relationships of biological macromolecules. The intrinsic value of suppression analysis is enhanced by advances in genomics and in biophysical techniques for investigating the properties of nucleic acids and proteins, such as X-ray crystallography, liquid and solid-state nuclear magnetic resonance, electron spin labeling, and isothermal calorimetry. These approaches confirm and complement whatever is revealed by genetics. Despite these sterling qualities, suppression analysis has its dangers, less in execution than in conceptualization of experiments and interpretation of data. A consistent nomenclature is essential for a uniform and widespread understanding of the results. Familiarity with the genetic background and idiosyncracies of the organism studied is critical in avoiding extraneous phenomena that can affect the outcome. Finally, it is imperative not to underestimate potentially bizarre and improbable consequences that can transpire when rigorous genetic selection is maintained for an appreciable length of time. The article begins with a somewhat pedagogical discussion of genetic terminology. It then moves on to the necessary precautions to observe while planning and conducting suppression analysis. The remainder of the article considers different manifestations of suppression: bypass suppression; gradients of suppression; suppression by relaxed specificity; allele-specific "suppression at a distance"; and true conformational suppression. The treatment is not exhaustive, but representative examples have been gleaned from the recent bacterial literature.
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Affiliation(s)
- M D Manson
- Department of Biology, Texas A&M University, College Station, Texas 77843, USA.
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24
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Kim KK, Yokota H, Kim SH. Four-helical-bundle structure of the cytoplasmic domain of a serine chemotaxis receptor. Nature 1999; 400:787-92. [PMID: 10466731 DOI: 10.1038/23512] [Citation(s) in RCA: 351] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The bacterial chemotaxis receptors are transmembrane receptors with a simple signalling pathway which has elements relevant to the general understanding of signal recognition and transduction across membranes, how signals are relayed between molecules in a pathway, and how adaptation to a persistent signal is achieved. In contrast to many mammalian receptors which signal by oligomerizing upon ligand binding, the chemotaxis receptors are dimeric even in the absence of their ligands, and their signalling does not depend on a monomer-dimer equilibrium. Bacterial chemotaxis receptors are composed of a ligand-binding domain, a transmembrane domain consisting of two helices TM1 and TM2, and a cytoplasmic domain. All known bacterial chemotaxis receptors have a highly conserved cytoplasmic domain, which unites signals from different ligand domains into a single signalling pathway to flagella motors. Here we report the crystal structure of the cytoplasmic domain of a serine chemotaxis receptor of Escherichia coli, which reveals a 200 A-long coiled-coil of two antiparallel helices connected by a 'U-turn'. Two of these domains form a long, supercoiled, four-helical bundle in the cytoplasmic portion of the receptor.
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Affiliation(s)
- K K Kim
- Department of Chemistry, University of California, Berkeley 94720-5230, USA
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25
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Aravind L, Ponting CP. The cytoplasmic helical linker domain of receptor histidine kinase and methyl-accepting proteins is common to many prokaryotic signalling proteins. FEMS Microbiol Lett 1999; 176:111-6. [PMID: 10418137 DOI: 10.1111/j.1574-6968.1999.tb13650.x] [Citation(s) in RCA: 295] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Mutations in the cytoplasmic linker regions of receptor histidine kinase and chemoreceptor proteins have been shown previously to significantly impair receptor functions. Here we demonstrate significant sequence similarities between these regions in numerous histidine kinases, methyl-accepting proteins, adenylyl cyclases and other prokaryotic signalling proteins. It is suggested that these 'HAMP domains' possess roles of regulating the phosphorylation or methylation of homodimeric receptors by transmitting the conformational changes in periplasmic ligand-binding domains to cytoplasmic signalling kinase and methyl-acceptor domains.
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Affiliation(s)
- L Aravind
- Department of Biology, Texas A&M University, College Station 70843, USA
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26
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Dang TA, Zhou XR, Graf B, Christie PJ. Dimerization of the Agrobacterium tumefaciens VirB4 ATPase and the effect of ATP-binding cassette mutations on the assembly and function of the T-DNA transporter. Mol Microbiol 1999; 32:1239-53. [PMID: 10383764 PMCID: PMC3918219 DOI: 10.1046/j.1365-2958.1999.01436.x] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
The Agrobacterium tumefaciens VirB4 ATPase functions with other VirB proteins to export T-DNA to susceptible plant cells and other DNA substrates to a variety of prokaryotic and eukaryotic cells. Previous studies have demonstrated that VirB4 mutants with defects in the Walker A nucleotide-binding motif are non-functional and exert a dominant negative phenotype when synthesized in wild-type cells. This study characterized the oligomeric structure of VirB4 and examined the effects of Walker A sequence mutations on complex formation and transporter activity. VirB4 directed dimer formation when fused to the amino-terminal portion of cI repressor protein, as shown by immunity of Escherichia coli cells to lambda phage infection. VirB4 also dimerized in Agrobacterium tumefaciens, as demonstrated by the recovery of a detergent-resistant complex of native protein and a functional, histidine-tagged derivative by precipitation with anti-His6 antibodies and by Co2+ affinity chromatography. Walker A sequence mutants directed repressor dimerization in E. coli and interacted with His-VirB4 in A. tumefaciens, indicating that ATP binding is not required for self-association. A dimerization domain was localized to a proposed N-terminal membrane-spanning region of VirB4, as shown by the dominance of an allele coding for the N-terminal 312 residues and phage immunity of host cells expressing cI repressor fusions to alleles for the first 237 or 312 residues. A recent study reported that the synthesis of a subset of VirB proteins, including VirB4, in agrobacterial recipients has a pronounced stimulatory effect on the virB-dependent conjugal transfer of plasmid RSF1010 by agrobacterial donors. VirB4'312 suppressed the stimulatory effect of VirB proteins for DNA uptake when synthesized in recipient cells. In striking contrast, Walker A sequence mutants contributed to the stimulatory effect of VirB proteins to the same extent as native VirB4. These findings indicate that the oligomeric structure of VirB4, but not its capacity to bind ATP, is important for the assembly of VirB proteins as a DNA uptake system. The results of these studies support a model in which VirB4 dimers or homomultimers contribute structural information for the assembly of a transenvelope channel competent for bidirectional DNA transfer, whereas an ATP-dependent activity is required for configuring this channel as a dedicated export machine.
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27
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Nishiyama SI, Umemura T, Nara T, Homma M, Kawagishi I. Conversion of a bacterial warm sensor to a cold sensor by methylation of a single residue in the presence of an attractant. Mol Microbiol 1999; 32:357-65. [PMID: 10231491 DOI: 10.1046/j.1365-2958.1999.01355.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The aspartate chemoreceptor (Tar) of Escherichia coli also serves as a thermosensor, and it is very amenable to genetic and biochemical analysis of the thermosensing mechanism. Its thermosensing properties are controlled by reversible methylation of the cytoplasmic signalling/adaptation domain of the protein. The unmethylated and the fully methylated (aspartate-bound) receptors sense, as attractant stimuli, increases (warm sensor) and decreases (cold sensor) in temperature respectively. To learn more about the mechanism of thermosensing, we replaced the four methyl-accepting glutamyl residues with non-methylatable aspartyl residues in all possible combinations. In a strain defective in both methyltransferase (CheR) and methylesterase (CheB) activities, all of the mutant Tar proteins functioned as warm sensors. To create a situation in which all of the remaining glutamyl residues were methylated, we expressed the mutant proteins in a CheB-defective, CheR-overproducing strain. The fully glutamyl-methylated proteins were designed to mimic the full range of methylation states possible for wild-type Tar. Almost all of the methylated mutant receptors, including those with single glutamyl residues, were cold sensors in the presence of aspartate. Thus, binding of aspartate to Tar and methylation of its single glutamyl residue can invert its temperature-dependent signalling properties.
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Affiliation(s)
- S I Nishiyama
- Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan
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28
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Nishiyama S, Maruyama IN, Homma M, Kawagishi I. Inversion of thermosensing property of the bacterial receptor Tar by mutations in the second transmembrane region. J Mol Biol 1999; 286:1275-84. [PMID: 10064695 DOI: 10.1006/jmbi.1999.2555] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The aspartate chemoreceptor Tar of Escherichia coli serves as a warm sensor that produces attractant and repellent signals upon increases and decreases in temperature, respectively. However, increased levels of methylation of the cytoplasmic domain of Tar resulting from aspartate binding convert Tar to a cold sensor with the opposite signaling behavior. Detailed analyses of the methylation sites, which are located in two separate alpha-helices (MH1 and MH2), have suggested that intra- and/or intersubunit interactions of MH1 and MH2 play a critical role in thermosensing. These interactions may be influenced by binding of aspartate, which could trigger some displacement of MH1 through the second transmembrane region (TM2). As an initial step toward understanding the role of TM2 in thermosensing, we have examined the thermosensing properties of 43 mutant Tar receptors with randomized TM2 sequences (residues 190-210). Among them, we identified one mutant receptor (Tar-I2) that functioned as a cold sensor in the absence of aspartate. This is the first example of attractant-independent inversion of thermosensing in Tar. Further analyses identified the minimal essential divergence from the wild-type Tar sequence (Q191V-W192R-Q193C) required for the inverted response. Thus, displacements of TM2 seem to influence the thermosensing function of Tar.
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Affiliation(s)
- S Nishiyama
- Division of Biological Science Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya, 464-8602, Japan
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29
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Zhang Y, Gardina PJ, Kuebler AS, Kang HS, Christopher JA, Manson MD. Model of maltose-binding protein/chemoreceptor complex supports intrasubunit signaling mechanism. Proc Natl Acad Sci U S A 1999; 96:939-44. [PMID: 9927672 PMCID: PMC15329 DOI: 10.1073/pnas.96.3.939] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The Tar protein of Escherichia coli is unique among known bacterial chemoreceptors in that it generates additive responses to two very disparate ligands, aspartate and maltose. Aspartate binds directly to the periplasmic (extracytoplasmic) domain of Tar. Maltose first binds to maltose-binding protein (MBP). MBP then assumes a closed conformation in which it can interact with the periplasmic domain of Tar. MBP residues critical for binding Tar were identified in a screen of mutations that cause specific defects in maltose chemotaxis. Mutations were introduced into a plasmid-borne malE gene that encodes a mutant form of MBP in which two engineered Cys residues spontaneously generate a disulfide bond in the oxidizing environment of the periplasmic space. This disulfide covalently crosslinks the NH3-terminal and COOH-terminal domains of MBP and locks the protein into a closed conformation. Double-Cys MBP confers a dominant-negative phenotype for maltose taxis, and we reasoned that third mutations that relieve this negative dominance probably alter residues that are important for the initial interaction of MBP with Tar. The published three-dimensional structures of MBP and the periplasmic domain of E. coli Tar were docked in a computer simulation that juxtaposed the residues in MBP identified in this way with residues in Tar that have been implicated in maltose taxis. The resulting model of the MBP-Tar complex exhibits good complementarity between the surfaces of the two proteins and supports the idea that aspartate and MBP may each initiate an attractant signal through Tar by inducing similar conformational changes in the chemoreceptor.
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Affiliation(s)
- Y Zhang
- Department of Biology, Texas A&M University, College Station, TX 77843, USA
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30
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Trammell MA, Falke JJ. Identification of a site critical for kinase regulation on the central processing unit (CPU) helix of the aspartate receptor. Biochemistry 1999; 38:329-36. [PMID: 9890914 PMCID: PMC2899683 DOI: 10.1021/bi981964u] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Ligand binding to the homodimeric aspartate receptor of Escherichia coli and Salmonella typhimurium generates a transmembrane signal that regulates the activity of a cytoplasmic histidine kinase, thereby controlling cellular chemotaxis. This receptor also senses intracellular pH and ambient temperature and is covalently modified by an adaptation system. A specific helix in the cytoplasmic domain of the receptor, helix alpha6, has been previously implicated in the processing of these multiple input signals. While the solvent-exposed face of helix alpha6 possesses adaptive methylation sites known to play a role in kinase regulation, the functional significance of its buried face is less clear. This buried region lies at the subunit interface where helix alpha6 packs against its symmetric partner, helix alpha6'. To test the role of the helix alpha6-helix alpha6' interface in kinase regulation, the present study introduces a series of 13 side-chain substitutions at the Gly 278 position on the buried face of helix alpha6. The substitutions are observed to dramatically alter receptor function in vivo and in vitro, yielding effects ranging from kinase superactivation (11 examples) to complete kinase inhibition (one example). Moreover, four hydrophobic, branched side chains (Val, Ile, Phe, and Trp) lock the kinase in the superactivated state regardless of whether the receptor is occupied by ligand. The observation that most side-chain substitutions at position 278 yield kinase superactivation, combined with evidence that such facile superactivation is rare at other receptor positions, identifies the buried Gly 278 residue as a regulatory hotspot where helix packing is tightly coupled to kinase regulation. Together, helix alpha6 and its packing interactions function as a simple central processing unit (CPU) that senses multiple input signals, integrates these signals, and transmits the output to the signaling subdomain where the histidine kinase is bound. Analogous CPU elements may be found in other receptors and signaling proteins.
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31
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Abstract
Recent biochemical and structural studies have provided many new insights into the structure and function of bacterial chemoreceptors. Aspects of their ligand binding, conformational changes, and interactions with other members of the signaling pathway are being defined at the structural level. It is anticipated that the combined effort will soon provide a detailed, unified view of an entire response system.
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Affiliation(s)
- S L Mowbray
- Department of Molecular Biology, Swedish Agricultural University, Upsala, Sweden.
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32
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Umemura T, Tatsuno I, Shibasaki M, Homma M, Kawagishi I. Intersubunit interaction between transmembrane helices of the bacterial aspartate chemoreceptor homodimer. J Biol Chem 1998; 273:30110-5. [PMID: 9804765 DOI: 10.1074/jbc.273.46.30110] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The transmembrane domain that connects the extracellular and intracellular domains of cell-surface receptors must play a critical role in signal transduction. Here, we report studies of the interaction between the transmembrane helices (TM1 and TM2) of the Escherichia coli aspartate chemoreceptor (Tar). Tar exists as a homodimer regardless of its state of ligand occupancy. A particular residue substitution in TM1 (A19K) abolishes the signaling ability of Tar. This signaling defect can be suppressed by single residue substitutions in TM2 (W192R, A198E, V201E, and V202L). We have found that these suppressors can be divided into two groups. A198E and V201E (class 1) almost completely suppress the defects caused by A19K, and this suppression occurs between two subunits of the Tar dimer. In contrast, W192R and V202L (class 2) fail to suppress some signaling defects, and their suppression does not occur between subunits. Because disulfide-crosslinking studies predict that residues 198 and 201 point toward residue 19 of the partner subunit, we propose that the class 1 suppressors form an intersubunit salt bridge with Lys-19. Indeed, A19K was suppressed by several additional aspartate or glutamate substitutions on the same face of TM2 occupied by residues 198 and 201. None of these intersubunit salt bridges perturb signaling function, suggesting that the mechanism of transmembrane signal propagation does not involve large displacements (such as extensive rotation) of the TM1 and TM2 helices relative to each other.
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Affiliation(s)
- T Umemura
- Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan
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33
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Levit MN, Liu Y, Stock JB. Stimulus response coupling in bacterial chemotaxis: receptor dimers in signalling arrays. Mol Microbiol 1998; 30:459-66. [PMID: 9822812 DOI: 10.1046/j.1365-2958.1998.01066.x] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In the Escherichia coli chemotaxis system, a family of chemoreceptors in the cytoplasmic membrane binds stimulatory ligands and regulates the activity of an associated histidine kinase CheA to modulate swimming behaviour and thereby cause a net migration towards attractants and away from repellents. The chemoreceptors themselves have been shown to be predominantly dimeric, but in the presence of the kinase CheA plus an adapter protein, CheW, much higher order structures have been observed. Recent results indicate that transmembrane signalling occurs within receptor clusters rather than through isolated dimers. We propose that the mechanism involves receptor arrays where binding of ligands at the outside surface of the membrane affects lateral packing interactions that cause perturbations in the organization of the signalling array at the opposing surface of the membrane. Results with receptor chimeras as well as findings with tyrosine kinase receptors suggest that this mechanism may represent a common theme in membrane receptor function.
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Affiliation(s)
- M N Levit
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
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34
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Gardina PJ, Bormans AF, Manson MD. A mechanism for simultaneous sensing of aspartate and maltose by the Tar chemoreceptor of Escherichia coli. Mol Microbiol 1998; 29:1147-54. [PMID: 9767583 DOI: 10.1046/j.1365-2958.1998.00964.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The Tar chemoreceptor of Escherichia coli exhibits partial sensory additivity. Tar can mediate simultaneous responses to two disparate ligands, aspartate and substrate-loaded maltose-binding protein (MBP). To investigate how one receptor generates concurrent signals to two stimuli, ligand-binding asymmetry was imposed on the rotationally symmetric Tar homodimer. Mutations causing specific defects in aspartate or maltose chemotaxis were introduced pairwise into plasmid-borne tar genes. The doubly mutated tar genes did not restore aspartate or maltose chemotaxis in a strain containing a chromosomal deletion of tar (delta tar). However, when Tar proteins with complementing sets of mutations were co-expressed from compatible plasmids, the resulting heterodimeric receptors enabled delta tar cells to respond to aspartate or maltose. The effect of one attractant on the response to the other depended on the relative orientations of the functional binding sites for aspartate and MBP. When the sites were in the 'same' orientation, saturating levels of one attractant strongly inhibited chemotaxis to the other. In the 'opposite' orientation, such inhibitory effects were negligible. These data demonstrate that opposing subunits of Tar can transmit signals to aspartate and maltose independently if the ligands are restricted to the 'opposite' binding orientation. When aspartate and MBP bind in the 'same' orientation, they compete for signalling through one subunit. In the wild-type Tar dimer, aspartate and MBP can bind in either the 'same' or the 'opposite' orientation, a freedom that can explain the partial additivity of the aspartate and maltose responses that is seen with tar+ cells.
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Affiliation(s)
- P J Gardina
- Department of Biology, Texas A&M University, College Station 77843-3258, USA
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35
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Zhang XN, Spudich JL. HtrI is a dimer whose interface is sensitive to receptor photoactivation and His-166 replacements in sensory rhodopsin I. J Biol Chem 1998; 273:19722-8. [PMID: 9677402 DOI: 10.1074/jbc.273.31.19722] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Single cysteine substitutions were introduced into three positions of otherwise cysteineless HtrI, a phototaxis transducer found in Halobacterium salinarum that transmits signals from the photoreceptor sensory rhodopsin I (SRI) to a cytoplasmic pathway controlling the cell's motility. Oxidative cross-linking of the monocysteine HtrI mutants in membrane suspensions resulted in dimer forms evident in SDS-polyacrylamide gels. The rate of cross-linking of I64C on the cytoplasmic side of HtrI was accelerated by SRI binding in the dark and further increased by SRI photoactivation. Several residue replacements of His-166 in SRI accelerated the cross-linking rate of I64C in the dark and His-166 mutants that exhibit "inverted signaling" (mediating repellent instead of the normally attractant response to orange light) inverted the light effect on the cross-linking rate of I64C. Secondary structure prediction of HtrI indicates a coiled coil structure in the cytoplasmic region following TM2, a dimerization domain found in a diverse group of proteins. We conclude that 1) HtrI exists as a dimer both in the absence of SRI and in the SRI-HtrI complex, 2) binding of SRI in the dark increases reactivity of the two cysteines at position 64 in the dimer by increasing their proximity or mobility, 3) light activation of wild-type SRI further increases their reactivity, 4) His-166 replacements in the SRI receptor have conformational effects on the structure of HtrI at position 64, and 5) inverted signaling by His-166 mutants likely results from an inverted conformational change at this region induced by SRI photoactivation.
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Affiliation(s)
- X N Zhang
- Department of Microbiology and Molecular Genetics, University of Texas Medical School, Houston, Texas 77030, USA
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36
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Butler SL, Falke JJ. Cysteine and disulfide scanning reveals two amphiphilic helices in the linker region of the aspartate chemoreceptor. Biochemistry 1998; 37:10746-56. [PMID: 9692965 PMCID: PMC2899697 DOI: 10.1021/bi980607g] [Citation(s) in RCA: 98] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The transmembrane aspartate receptor of E. coli and S. typhimurium mediates cellular chemotaxis toward aspartate by regulating the activity of the cytoplasmic histidine kinase, CheA. Ligand binding results in transduction of a conformational signal through the membrane to the cytoplasmic domain where both kinase regulation and adaptation occur. Of particular interest is the linker region, E213 to Q258, which connects and transduces the conformational signal between the cytoplasmic end of the transmembrane signaling helix (alpha 4/TM2) and the major methylation helix of the cytoplasmic domain (alpha 6). This linker is crucial for stable folding and function of the homodimeric receptor. The present study uses cysteine and disulfide scanning mutagenesis to investigate the secondary structure and packing surfaces within the linker region. Chemical reactivity assays reveal that the linker consists of three distinct subdomains: two alpha-helices termed alpha 4 and alpha 5 and, between them, an ordered region of undetermined secondary structure. When cysteine is scanned through the helices, characteristic repeating patterns of solvent exposure and burial are observed. Activity assays, both in vivo and in vitro, indicate that each helix possesses a buried packing face that is crucial for proper receptor function. The interhelical subdomain is at least partially buried and is also crucial for proper receptor function. Disulfide scanning places helix alpha 4 distal to the central axis of the homodimer, while helix alpha 5 is found to lie at the subunit interface. Finally, sequence alignments suggest that all three linker subdomains are highly conserved among the large subfamily of histidine kinase-coupled sensory receptors that possess methylation sites for use in covalent adaptation.
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Affiliation(s)
| | - Joseph J. Falke
- Corresponding author. Telephone: 303-492-3503. Fax: 303-492-5894.
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37
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Park H, Saha SK, Inouye M. Two-domain reconstitution of a functional protein histidine kinase. Proc Natl Acad Sci U S A 1998; 95:6728-32. [PMID: 9618480 PMCID: PMC22614 DOI: 10.1073/pnas.95.12.6728] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
In prokaryotes, in the absence of protein serine/threonine/tyrosine kinases, protein histidine kinases play a major role in signal transduction involved in cellular adaptation to various environmental changes and stresses. Histidine kinases phosphorylate their cognate response regulators at a specific aspartic acid residue with ATP in response to particular environmental signals. In this His-Asp phosphorelay signal transduction system, it is still unknown how the histidine kinase exerts its enzymatic function. Here we demonstrate that the cytoplasmic kinase domain of EnvZ, a transmembrane osmosensor of Escherichia coli can be further divided into two distinct functional subdomains: subdomain A [EnvZ(C). (223-289); 67 residues] and subdomain B [EnvZ(C).(290-450); 161 residues]. Subdomain A, with a high helical content, contains the autophosphorylation site, H-243, and forms a stable dimer having the recognition site for OmpR, the cognate response regulator of EnvZ. Subdomain B, an alpha/beta-protein, exists as a monomer. When mixed, the two subdomains reconstitute the kinase function to phosphorylate subdomain A at His-243 in the presence of ATP. Subsequently, the phosphorylated subdomain A is able to transfer its phosphate group to OmpR. The two-domain structure of this histidine kinase provides an insight into the structural arrangement of the enzyme and its transphosphorylation mechanism.
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Affiliation(s)
- H Park
- Department of Biochemistry, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, 675 Hoes Lane, Piscataway, NJ 08854-5635, USA
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38
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Jones DH, Barber KR, Grant CW. Sequence-related behaviour of transmembrane domains from class I receptor tyrosine kinases. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1371:199-212. [PMID: 9630629 DOI: 10.1016/s0005-2736(98)00015-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
2H NMR spectroscopy and freeze-fracture electron microscopy were used to compare the transmembrane domains of two Class I protein receptor tyrosine kinases (the EGF receptor and Neu/erbB-2) regarding overall behaviour in fluid lipid bilayer membranes. The 34-residue peptide, EGFRtm, was synthesised to contain the 23 amino acid hydrophobic stretch (Ile622 to Met644) thought to span the membrane of the human EGF receptor, plus the first 10 amino acids (Arg645 to Thr654) of the cytoplasmic domain. Deuterium probes replaced selected 1H nuclei at sites corresponding to Ala623, Met644, and Val650. The 38-residue peptide, Neutm, was synthesised having the 21 residue hydrophobic stretch (Ile660 to Ile680) calculated to span the membrane in rat Neu/erbB-2, plus residues Lys681 to Thr691 of the contiguous cytoplasmic domain. Deuterium probes replaced selected 1H nuclei at Ala661, Leu667, and Val676. A third peptide, Neutm*, was also prepared, corresponding to the transmembrane domain of a constitutively-activating Neu/erbB-2 transformant in which Val664 is replaced by Glu: it was deuterated in a manner identical to Neutm. Peptides were studied by 2H NMR spectroscopy at 1 mol% and 6 mol% in unsonicated fluid bilayers of 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) and in POPC containing 33 mol% cholesterol, over the range 12 degrees to 65 degreesC. Overall motion was found to be different for each of the three peptides under a given set of conditions. EGFRtm spectra were characteristic of axially symmetric motion in membranes of POPC alone, and in POPC/cholesterol at 35 degreesC and above. In contrast, spectra of the transmembrane peptides, Neutm and Neutm*, were characteristic of significantly axially asymmetric motion under all conditions studied (and regardless of sample preparation method). Addition of 33% cholesterol to membranes was accompanied by spectral changes consistent with increased formation of peptide dimers/oligomers in all cases. The transformant peptide, Neutm*, showed greater spectral evidence of immobilisation than did the wild type - probably reflecting a greater tendency to form large oligomers. Sequence-related details within the transmembrane domains of Class I receptor tyrosine kinases appear to exert important control over their associations within membranes. Freeze-fracture electron microscopy of the NMR samples demonstrated their liposomal nature. Peptide-related intramembranous particles (IMPs) were present which likely represent oligomers of the transmembrane peptide. IMP size and distribution were similar under a given set of conditions for all three peptides, suggesting that the differences seen by NMR spectroscopy reflect structures smaller than the 2 nm resolution limit of freeze-fracture EM and peptide relationships within its 20 nm accuracy of identifying lateral position.
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Affiliation(s)
- D H Jones
- Department of Biochemistry, University of Western Ontario, London, Canada
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39
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Jung KH, Spudich JL. Suppressor mutation analysis of the sensory rhodopsin I-transducer complex: insights into the color-sensing mechanism. J Bacteriol 1998; 180:2033-42. [PMID: 9555883 PMCID: PMC107127 DOI: 10.1128/jb.180.8.2033-2042.1998] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The molecular complex containing the phototaxis receptor sensory rhodopsin I (SRI) and transducer protein HtrI (halobacterial transducer for SRI) mediates color-sensitive phototaxis responses in the archaeon Halobacterium salinarum. One-photon excitation of the complex by orange light elicits attractant responses, while two-photon excitation (orange followed by near-UV light) elicits repellent responses in swimming cells. Several mutations in SRI and HtrI cause an unusual mutant phenotype, called orange-light-inverted signaling, in which the cell produces a repellent response to normally attractant light. We applied a selection procedure for intragenic and extragenic suppressors of orange-light-inverted mutants and identified 15 distinct second-site mutations that restore the attractant response. Two of the 3 suppressor mutations in SRI are positioned at the cytoplasmic ends of helices F and G, and 12 suppressor mutations in HtrI cluster at the cytoplasmic end of the second HtrI transmembrane helix (TM2). Nearly all suppressors invert the normally repellent response to two-photon stimulation to an attractant response when they are expressed with their suppressible mutant alleles or in an otherwise wild-type strain. The results lead to a model for control of flagellar reversal by the SRI-HtrI complex. The model invokes an equilibrium between the A (reversal-inhibiting) and R (reversal-stimulating) conformers of the signaling complex. Attractant light and repellent light shift the equilibrium toward the A and R conformers, respectively, and mutations are proposed to cause intrinsic shifts in the equilibrium in the dark form of the complex. Differences in the strength of the two-photon signal inversion and in the allele specificity of suppression are correlated, and this correlation can be explained in terms of different values of the equilibrium constant (Keq) for the conformational transition in different mutants and mutant-suppressor pairs.
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Affiliation(s)
- K H Jung
- Department of Microbiology and Molecular Genetics, University of Texas-Houston Medical School, 77030, USA
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40
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Goudreau PN, Stock AM. Signal transduction in bacteria: molecular mechanisms of stimulus-response coupling. Curr Opin Microbiol 1998; 1:160-9. [PMID: 10066483 DOI: 10.1016/s1369-5274(98)80006-4] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In bacteria, adaptive responses to changing environmental conditions are mediated by signal transduction systems that involve modular protein domains. Despite great diversity in the integration of domains into different systems, studies of individual components have revealed molecular strategies that are widely applicable. Studies of receptors have advanced our understanding of how information is transmitted across membranes, the determination of three-dimensional structures of domains of histidine protein kinase domains and response regulator proteins has begun to reveal the molecular basis of signaling via two-component phosphoryltransfer pathways, and the description of 'eukaryotic-like' protein domains involved in bacterial signaling has emphasized the universality of intracellular signaling mechanisms.
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Affiliation(s)
- P N Goudreau
- Center for Advanced Biotechnology and Medicine, Howard Hughes Medical Institute, University of Medicine and Dentistry of New Jersey, 679 HoesLane, Piscataway, NJ 08854-5638, USA.
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41
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Singer KL, Mostov KE. Dimerization of the polymeric immunoglobulin receptor controls its transcytotic trafficking. Mol Biol Cell 1998; 9:901-15. [PMID: 9529387 PMCID: PMC25316 DOI: 10.1091/mbc.9.4.901] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Binding of dimeric immunoglobulin (Ig)A to the polymeric Ig receptor (pIgR) stimulates transcytosis of pIgR across epithelial cells. Through the generation of a series of pIgR chimeric constructs, we have tested the ability of ligand to promote receptor dimerization and the subsequent role of receptor dimerization on its intracellular trafficking. Using the cytoplasmic domain of the T cell receptor-zeta chain as a sensitive indicator of receptor oligomerization, we show that a pIgR:zeta chimeric receptor expressed in Jurkat cells initiates a zeta-specific signal transduction cascade when exposed to dimeric or tetrameric IgA, but not when exposed to monomeric IgA. In addition, we replaced the pIgR's transmembrane domain with that of glycophorin A to force dimerization or with a mutant glycophorin transmembrane domain to prevent dimerization. Forcing dimerization stimulated transcytosis of the chimera, whereas preventing dimerization abolished ligand-stimulated transcytosis. We conclude that binding of dimeric IgA to the pIgR induces its dimerization and that this dimerization is necessary and sufficient to stimulate pIgR transcytosis.
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Affiliation(s)
- K L Singer
- Department of Anatomy and Department of Biochemistry and Biophysics, and Cardiovascular Research Institute, University of California, San Francisco, California 94143-0452, USA
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42
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Okumura H, Nishiyama S, Sasaki A, Homma M, Kawagishi I. Chemotactic adaptation is altered by changes in the carboxy-terminal sequence conserved among the major methyl-accepting chemoreceptors. J Bacteriol 1998; 180:1862-8. [PMID: 9537386 PMCID: PMC107101 DOI: 10.1128/jb.180.7.1862-1868.1998] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
In Escherichia coli and Salmonella typhimurium, methylation and demethylation of receptors are responsible for chemotactic adaptation and are catalyzed by the methyltransferase CheR and the methylesterase CheB, respectively. Among the chemoreceptors of these species, Tsr, Tar, and Tcp have a well-conserved carboxy-terminal motif (NWET/SF) that is absent in Trg and Tap. When they are expressed as sole chemoreceptors, Tsr, Tar, and Tcp support good adaptation, but Trg and Tap are poorly methylated and supported only weak adaptation. It was recently discovered that CheR binds to the NWETF sequence of Tsr in vitro. To examine the physiological significance of this binding, we characterized mutant receptors in which this pentapeptide sequence was altered. C-terminally-mutated Tar and Tcp expressed in a receptorless E. coli strain mediated responses to aspartate and citrate, respectively, but their adaptation abilities were severely impaired. Their expression levels and attractant-sensing abilities were similar to those of the wild-type receptors, but the methylation levels of the mutant receptors increased only slightly upon addition of attractants. When CheR was overproduced, both the adaptation and methylation profiles of the mutant Tar receptor became comparable to those of wild-type Tar. Furthermore, overproduction of CheR also enhanced adaptive methylation of wild-type Trg, which lacks the NWETF sequence, in the absence of any other chemoreceptor. These results suggest that the pentapeptide sequence facilitates effective adaptation and methylation by recruiting CheR.
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Affiliation(s)
- H Okumura
- Division of Biological Science, Graduate School of Science, Nagoya University, Japan
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43
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Abstract
The components of the Escherichia coli chemosensory system have been identified and their activities characterized, but how sensory information is processed to give an integrated response remains an open question.
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Affiliation(s)
- T W Grebe
- Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544, USA
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44
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Domanski P, Nadeau OW, Platanias LC, Fish E, Kellum M, Pitha P, Colamonici OR. Differential use of the betaL subunit of the type I interferon (IFN) receptor determines signaling specificity for IFNalpha2 and IFNbeta. J Biol Chem 1998; 273:3144-7. [PMID: 9452423 DOI: 10.1074/jbc.273.6.3144] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The signaling specificity for cytokines that have common receptor subunits is achieved by the presence of additional cytokine-specific receptor components. In the type I interferon (IFN) family, all 14 subtypes of IFNalpha, IFNbeta, and IFNomega bind to the same alpha and betaL subunits of the type I IFN-R, yet differences in signaling and biological effects exist among them. Our data demonstrate that IFNalpha2 and IFNbeta utilize different regions of the betaL subunit for signaling. Thus, in contrast to other cytokine systems, signal diversity in the type I IFN system can be accomplished within the same receptor complex by utilizing different regions of the same receptor subunits.
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Affiliation(s)
- P Domanski
- Department of Pathology, University of Tennessee, Memphis, Tennessee 38163, USA
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45
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Liu Y, Levit M, Lurz R, Surette MG, Stock JB. Receptor-mediated protein kinase activation and the mechanism of transmembrane signaling in bacterial chemotaxis. EMBO J 1997; 16:7231-40. [PMID: 9405352 PMCID: PMC1170323 DOI: 10.1093/emboj/16.24.7231] [Citation(s) in RCA: 110] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Chemotaxis responses of Escherichia coli and Salmonella are mediated by type I membrane receptors with N-terminal extracytoplasmic sensing domains connected by transmembrane helices to C-terminal signaling domains in the cytoplasm. Receptor signaling involves regulation of an associated protein kinase, CheA. Here we show that kinase activation by a soluble signaling domain construct involves the formation of a large complex, with approximately 14 receptor signaling domains per CheA dimer. Electron microscopic examination of these active complexes indicates a well defined bundle composed of numerous receptor filaments. Our findings suggest a mechanism for transmembrane signaling whereby stimulus-induced changes in lateral packing interactions within an array of receptor-sensing domains at the cell surface perturb an equilibrium between active and inactive receptor-kinase complexes within the cytoplasm.
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Affiliation(s)
- Y Liu
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
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46
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Nimchinsky EA, Hof PR, Janssen WG, Morrison JH, Schmauss C. Expression of dopamine D3 receptor dimers and tetramers in brain and in transfected cells. J Biol Chem 1997; 272:29229-37. [PMID: 9361002 DOI: 10.1074/jbc.272.46.29229] [Citation(s) in RCA: 120] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The expression and characteristics of the dopamine D3 receptor protein were studied in brain and in stably transfected GH3 cells. Monoclonal antibodies were used for immunoprecipitation and immunoblot experiments. Immunoprecipitates obtained from primate and rodent brain tissues contain a low molecular weight D3 protein and one or two larger protein species whose molecular mass are integral multiples of the low molecular weight protein and thus appear to have resulted from dimerization and tetramerization of a D3 monomer. Whereas D3 receptor multimers were found to be abundantly expressed in brain, the major D3 immunoreactivity expressed in stable D3-expressing rat GH3 cells was found to be a monomer. However, multimeric D3 receptor species with electrophoretic mobilities similar to those expressed in brain were also seen in D3-expressing GH3 cells when a truncated D3-like protein (named D3nf) was co-expressed in these cells. Furthermore, results from immunoprecipitation experiments with D3- and D3nf-specific antibodies show that the higher-order D3 proteins extracted from brain and D3/D3nf double transfectants also contain D3nf immunoreactivity, and immunocytochemical studies show that the expression of D3 and D3nf immunoreactivities overlaps substantially in monkey and rat cortical neurons. Altogether, these data show oligomeric D3 receptor protein expression in vivo and they suggest that at least some of these oligomers are heteroligomeric protein complexes containing D3 and the truncated D3nf protein.
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Affiliation(s)
- E A Nimchinsky
- Fishberg Research Center for Neurobiology and Neurobiology of Aging Laboratories, Mount Sinai School of Medicine, New York, New York 10029, USA
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47
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Nishiyama S, Nara T, Homma M, Imae Y, Kawagishi I. Thermosensing properties of mutant aspartate chemoreceptors with methyl-accepting sites replaced singly or multiply by alanine. J Bacteriol 1997; 179:6573-80. [PMID: 9352902 PMCID: PMC179581 DOI: 10.1128/jb.179.21.6573-6580.1997] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The aspartate chemoreceptor Tar has a thermosensing function that is modulated by covalent modification of its four methylation sites (Gln295, Glu302, Gln309, and Glu491). Without posttranslational deamidation, Tar has no thermosensing ability. When Gln295 and Gln309 are deamidated to Glu, the unmethylated and heavily methylated forms function as warm and cold sensors, respectively. In this study, we carried out alanine-scanning mutagenesis of the methylation sites. Although alanine substitutions influenced the signaling bias and the methylation level, all of the mutants retained aspartate-sensing function. Those with single substitutions had almost normal thermosensing properties, indicating that substitutions at any particular methylation site do not seriously impair thermosensing function. In the posttranslational modification-defective background, some of the alanine substitutions restored thermosensing ability. Warm sensors were found among mutants retaining two glutamate residues, and cold sensors were found among those with one or no glutamate residue. This result suggests that the negative charge at the methylation sites is one factor that determines thermosensor phenotypes, although the size and shape of the side chain may also be important. The warm, cold, and null thermosensor phenotypes were clearly differentiated, and no intermediate phenotypes were found. Thus, the different thermosensing phenotypes that result from covalent modification of the methylation sites may reflect distinct structural states. Broader implications for the thermosensing mechanism are also discussed.
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Affiliation(s)
- S Nishiyama
- Division of Biological Science, Graduate School of Science, Nagoya University, Japan
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48
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Ottemann KM, Koshland DE. Converting a transmembrane receptor to a soluble receptor: recognition domain to effector domain signaling after excision of the transmembrane domain. Proc Natl Acad Sci U S A 1997; 94:11201-4. [PMID: 9326586 PMCID: PMC23415 DOI: 10.1073/pnas.94.21.11201] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The bacterial aspartate receptor was reconstructed to eliminate the transmembrane domain, thus connecting the recognition domain directly to the effector domain. The resulting soluble receptor folded correctly and was no longer an integral membrane protein. Upon aspartate binding, this soluble receptor was stabilized to a similar extent as that of the native receptor. Of interest, this soluble receptor retained the ability to signal from the recognition to the effector domain. This result defines more clearly the role of the membrane and transmembrane domains in signal transduction and suggests that some ligand-induced motions in receptor proteins do not require the membrane or transmembrane domain for information transmission.
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Affiliation(s)
- K M Ottemann
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3206, USA
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49
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Chi YI, Yokota H, Kim SH. Apo structure of the ligand-binding domain of aspartate receptor from Escherichia coli and its comparison with ligand-bound or pseudoligand-bound structures. FEBS Lett 1997; 414:327-32. [PMID: 9315712 DOI: 10.1016/s0014-5793(97)01027-2] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The aspartate receptor from E. coli is a dimeric transmembrane-signaling protein that mediates chemotaxis behavior and is the most studied system among the chemotaxis receptors to understand the molecular mechanism for transmembrane signaling. However, there is an unresolved issue for the structural event which initiates the transmembrane signal upon binding to the ligand. Biochemical and genetic evidence implies an intrasubunit mechanism (monomeric model) whereas crystallographic evidence implies an intersubunit mechanism (dimeric model). Crystallographic evidence has been ambiguous because all the apo protein structures contained a pseudoligand sulfate, and a completely ligand-free structure has not been available thus far. Here we present the crystal structure of the ligand binding domain of the aspartate receptor free of the ligand aspartate or pseudoligand sulfate. The structural comparison of this structure with those of ligand-bound and pseudoligand-bound forms revealed that, on ligand or pseudoligand binding, the conformational change in the ligand-binding domain is relatively small, but there is a considerable rotation between two subunits, supporting the dimeric model.
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Affiliation(s)
- Y I Chi
- Department of Chemistry and Lawrence Berkeley National Laboratory, University of California, Berkeley 94720, USA
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50
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Iwama T, Homma M, Kawagishi I. Uncoupling of ligand-binding affinity of the bacterial serine chemoreceptor from methylation- and temperature-modulated signaling states. J Biol Chem 1997; 272:13810-5. [PMID: 9153237 DOI: 10.1074/jbc.272.21.13810] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The Escherichia coli chemoreceptor Tsr mediates tactic responses to serine, repellents, and changes in temperature. We have previously shown that the serine-sensing ability of Tsr-T156C, which has a unique cysteine in place of threonine at residue 156, is specifically inactivated by thiol-modifying reagents and that L-serine protects the receptor from modification. In this study, we demonstrated the correlation between protective effects of various attractants and their potencies to elicit attractant responses. This indirect binding assay was used to monitor the affinity of the receptor for L-serine under various conditions. It has been demonstrated by in vitro assays that the ligand-binding affinities of Tsr and the related chemoreceptor Tar are unaffected by changes in the methylation state of the receptor. Using the serine protection assay, we re-examined this issue both in vitro and in vivo. The methylation levels of Tsr-T156C did not affect its ligand-binding affinity. We also showed both in vitro and in vivo that the ligand-binding affinity was unaffected by temperature. These results suggest that the structure of the periplasmic domain of the receptor is uncoupled from the signaling states of the cytoplasmic domain. This ligand-binding assay system should be applicable to other receptors.
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Affiliation(s)
- T Iwama
- Department of Biotechnology, Division of Utilization of Biological Resource, Faculty of Agriculture, Gifu University, Yanagido, Gifu 501-11, Japan
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