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Schneider T, Tan Y, Li H, Fisher JS, Zhang D. Photoglobin, a distinct family of non-heme binding globins, defines a potential photosensor in prokaryotic signal transduction systems. Comput Struct Biotechnol J 2022; 20:261-273. [PMID: 35024098 PMCID: PMC8717448 DOI: 10.1016/j.csbj.2021.12.022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2021] [Revised: 12/14/2021] [Accepted: 12/15/2021] [Indexed: 11/17/2022] Open
Abstract
Globins constitute an ancient superfamily of proteins, exhibiting enormous structural and functional diversity, as demonstrated by many heme-binding families and two non-heme binding families that were discovered in bacterial stressosome component RsbR and in light-harvesting phycobiliproteins (phycocyanin) in cyanobacteria and red algae. By comprehensively exploring the globin repertoire using sensitive computational analyses of sequences, structures, and genomes, we present the identification of the third family of non-heme binding globins—the photoglobin. By conducting profile-based comparisons, clustering analyses, and structural modeling, we demonstrate that photoglobin is related to, but distinct from, the phycocyanin family. Photoglobin preserves a potential ligand-binding pocket, whose residue configuration closely resembles that of phycocyanin, indicating that photoglobin potentially binds to a comparable linear tetrapyrrole. By exploring the contextual information provided by the photoglobin’s domain architectures and gene-neighborhoods, we found that photoglobin is frequently associated with the B12-binding light sensor domain and many domains typical of prokaryotic signal transduction systems. Structural modeling using AlphaFold2 demonstrated that photoglobin and B12-binding domains form a structurally conserved hub among different domain architecture contexts. Based on these strong associations, we predict that the coupled photoglobin and B12-binding domains act as a light-sensing regulatory bundle, with each domain sensing different wavelengths of light resulting in switch-like regulation of downstream signaling effectors. Thus, based on the above lines of evidence, we present a distinct non-heme binding globin family and propose that it may define a new type of light sensor, by means of a linear tetrapyrrole, in complex prokaryotic signal transduction systems.
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Affiliation(s)
- Theresa Schneider
- Department of Biology, College of Arts & Sciences, Saint Louis University, Saint Louis, MO 63105, United States
| | - Yongjun Tan
- Department of Biology, College of Arts & Sciences, Saint Louis University, Saint Louis, MO 63105, United States
| | - Huan Li
- Department of Biology, College of Arts & Sciences, Saint Louis University, Saint Louis, MO 63105, United States
| | - Jonathan S Fisher
- Department of Biology, College of Arts & Sciences, Saint Louis University, Saint Louis, MO 63105, United States
| | - Dapeng Zhang
- Department of Biology, College of Arts & Sciences, Saint Louis University, Saint Louis, MO 63105, United States.,Program of Bioinformatics and Computational Biology, College of Arts & Sciences, Saint Louis University, MO 63103, United States
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2
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Identification of Uncharacterized Components of Prokaryotic Immune Systems and Their Diverse Eukaryotic Reformulations. J Bacteriol 2020; 202:JB.00365-20. [PMID: 32868406 DOI: 10.1128/jb.00365-20] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Accepted: 08/25/2020] [Indexed: 12/19/2022] Open
Abstract
Nucleotide-activated effector deployment, prototyped by interferon-dependent immunity, is a common mechanistic theme shared by immune systems of several animals and prokaryotes. Prokaryotic versions include CRISPR-Cas with the CRISPR polymerase domain, their minimal variants, and systems with second messenger oligonucleotide or dinucleotide synthetase (SMODS). Cyclic or linear oligonucleotide signals in these systems help set a threshold for the activation of potentially deleterious downstream effectors in response to invader detection. We establish such a regulatory mechanism to be a more general principle of immune systems, which can also operate independently of such messengers. Using sensitive sequence analysis and comparative genomics, we identify 12 new prokaryotic immune systems, which we unify by this principle of threshold-dependent effector activation. These display regulatory mechanisms paralleling physiological signaling based on 3'-5' cyclic mononucleotides, NAD+-derived messengers, two- and one-component signaling that includes histidine kinase-based signaling, and proteolytic activation. Furthermore, these systems allowed the identification of multiple new sensory signal sensory components, such as a tetratricopeptide repeat (TPR) scaffold predicted to recognize NAD+-derived signals, unreported versions of the STING domain, prokaryotic YEATS domains, and a predicted nucleotide sensor related to receiver domains. We also identify previously unrecognized invader detection components and effector components, such as prokaryotic versions of the Wnt domain. Finally, we show that there have been multiple acquisitions of unidentified STING domains in eukaryotes, while the TPR scaffold was incorporated into the animal immunity/apoptosis signal-regulating kinase (ASK) signalosome.IMPORTANCE Both prokaryotic and eukaryotic immune systems face the dangers of premature activation of effectors and degradation of self-molecules in the absence of an invader. To mitigate this, they have evolved threshold-setting regulatory mechanisms for the triggering of effectors only upon the detection of a sufficiently strong invader signal. This work defines general templates for such regulation in effector-based immune systems. Using this, we identify several previously uncharacterized prokaryotic immune mechanisms that accomplish the regulation of downstream effector deployment by using nucleotide, NAD+-derived, two-component, and one-component signals paralleling physiological homeostasis. This study has also helped identify several previously unknown sensor and effector modules in these systems. Our findings also augment the growing evidence for the emergence of key animal immunity and chromatin regulatory components from prokaryotic progenitors.
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3
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Lessons from the post-genomic era: Globin diversity beyond oxygen binding and transport. Redox Biol 2020; 37:101687. [PMID: 32863222 PMCID: PMC7475203 DOI: 10.1016/j.redox.2020.101687] [Citation(s) in RCA: 38] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2020] [Revised: 08/11/2020] [Accepted: 08/11/2020] [Indexed: 12/16/2022] Open
Abstract
Vertebrate hemoglobin (Hb) and myoglobin (Mb) were among the first proteins whose structures and sequences were determined over 50 years ago. In the subsequent pregenomic period, numerous related proteins came to light in plants, invertebrates and bacteria, that shared the myoglobin fold, a signature sequence motif characteristic of a 3-on-3 α-helical sandwich. Concomitantly, eukaryote and bacterial globins with a truncated 2-on-2 α-helical fold were discovered. Genomic information over the last 20 years has dramatically expanded the list of known globins, demonstrating their existence in a limited number of archaeal genomes, a majority of bacterial genomes and an overwhelming majority of eukaryote genomes. In vertebrates, 6 additional globin types were identified, namely neuroglobin (Ngb), cytoglobin (Cygb), globin E (GbE), globin X (GbX), globin Y (GbY) and androglobin (Adgb). Furthermore, functions beyond the familiar oxygen transport and storage have been discovered within the vertebrate globin family, including NO metabolism, peroxidase activity, scavenging of free radicals, and signaling functions. The extension of the knowledge on globin functions suggests that the original roles of bacterial globins must have been enzymatic, involved in defense against NO toxicity, and perhaps also as sensors of O2, regulating taxis away or towards high O2 concentrations. In this review, we aimed to discuss the evolution and remarkable functional diversity of vertebrate globins with particular focus on the variety of non-canonical expression sites of mammalian globins and their according impressive variability of atypical functions.
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Prothmann A, Hoffmann FG, Opazo JC, Herbener P, Storz JF, Burmester T, Hankeln T. The Globin Gene Family in Arthropods: Evolution and Functional Diversity. Front Genet 2020; 11:858. [PMID: 32922435 PMCID: PMC7457136 DOI: 10.3389/fgene.2020.00858] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2020] [Accepted: 07/14/2020] [Indexed: 01/23/2023] Open
Abstract
Globins are small heme-proteins that reversibly bind oxygen. Their most prominent roles in vertebrates are the transport and storage of O2 for oxidative energy metabolism, but recent research has suggested alternative, non-respiratory globin functions. In the species-rich and ecologically highly diverse taxon of arthropods, the copper-containing hemocyanin is considered the main respiratory protein. However, recent studies have suggested the presence of globin genes and their proteins in arthropod taxa, including model species like Drosophila. To systematically assess the taxonomic distribution, evolution and diversity of globins in arthropods, we systematically searched transcriptome and genome sequence data and found a conserved, widespread occurrence of three globin classes in arthropods: hemoglobin-like (HbL), globin X (GbX), and globin X-like (GbXL) protein lineages. These globin types were previously identified in protostome and deuterostome animals including vertebrates, suggesting their early ancestry in Metazoa. The HbL genes show multiple, lineage-specific gene duplications in all major arthropod clades. Some HbL genes (e.g., Glob2 and 3 of Drosophila) display particularly fast substitution rates, possibly indicating the evolution of novel functions, e.g., in spermatogenesis. In contrast, arthropod GbX and GbXL globin genes show high evolutionary stability: GbXL is represented by a single-copy gene in all arthropod groups except Brachycera, and representatives of the GbX clade are present in all examined taxa except holometabolan insects. GbX and GbXL both show a brain-specific expression. Most arthropod GbX and GbXL proteins, but also some HbL variants, include sequence motifs indicative of potential N-terminal acylation (i.e., N-myristoylation, 3C-palmitoylation). All arthropods except for the brachyceran Diptera harbor at least one such potentially acylated globin copy, confirming the hypothesis of an essential, conserved globin function associated with the cell membrane. In contrast to other animals, the fourth ancient globin lineage, represented by neuroglobin, appears to be absent in arthropods, and the putative arthropod orthologs of the fifth metazoan globin lineage, androglobin, lack a recognizable globin domain. Thus, the remarkable evolutionary stability of some globin variants is contrasted by occasional dynamic gene multiplication or even loss of otherwise strongly conserved globin lineages in arthropod phylogeny.
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Affiliation(s)
- Andreas Prothmann
- Institute of Organismic and Molecular Evolution, Molecular Genetics and Genome Analysis, University of Mainz, Mainz, Germany
| | - Federico G Hoffmann
- Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology, Mississippi State University, Mississippi, MS, United States.,Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University, Mississippi, MS, United States
| | - Juan C Opazo
- Instituto de Ciencias Ambientales y Evolutivas, Facultad de Ciencias, Universidad Austral de Chile, Valdivia, Chile.,Millennium Nucleus of Ion Channels-Associated Diseases (MiNICAD), Valdivia, Chile
| | - Peter Herbener
- Institute of Organismic and Molecular Evolution, Molecular Genetics and Genome Analysis, University of Mainz, Mainz, Germany
| | - Jay F Storz
- School of Biological Sciences, University of Nebraska-Lincoln, Lincoln, NE, United States
| | | | - Thomas Hankeln
- Institute of Organismic and Molecular Evolution, Molecular Genetics and Genome Analysis, University of Mainz, Mainz, Germany
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Anantharaman K, Hausmann B, Jungbluth SP, Kantor RS, Lavy A, Warren LA, Rappé MS, Pester M, Loy A, Thomas BC, Banfield JF. Expanded diversity of microbial groups that shape the dissimilatory sulfur cycle. THE ISME JOURNAL 2018; 12:1715-1728. [PMID: 29467397 PMCID: PMC6018805 DOI: 10.1038/s41396-018-0078-0] [Citation(s) in RCA: 193] [Impact Index Per Article: 32.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/11/2017] [Revised: 01/10/2018] [Accepted: 01/13/2018] [Indexed: 11/16/2022]
Abstract
A critical step in the biogeochemical cycle of sulfur on Earth is microbial sulfate reduction, yet organisms from relatively few lineages have been implicated in this process. Previous studies using functional marker genes have detected abundant, novel dissimilatory sulfite reductases (DsrAB) that could confer the capacity for microbial sulfite/sulfate reduction but were not affiliated with known organisms. Thus, the identity of a significant fraction of sulfate/sulfite-reducing microbes has remained elusive. Here we report the discovery of the capacity for sulfate/sulfite reduction in the genomes of organisms from 13 bacterial and archaeal phyla, thereby more than doubling the number of microbial phyla associated with this process. Eight of the 13 newly identified groups are candidate phyla that lack isolated representatives, a finding only possible given genomes from metagenomes. Organisms from Verrucomicrobia and two candidate phyla, Candidatus Rokubacteria and Candidatus Hydrothermarchaeota, contain some of the earliest evolved dsrAB genes. The capacity for sulfite reduction has been laterally transferred in multiple events within some phyla, and a key gene potentially capable of modulating sulfur metabolism in associated cells has been acquired by putatively symbiotic bacteria. We conclude that current functional predictions based on phylogeny significantly underestimate the extent of sulfate/sulfite reduction across Earth's ecosystems. Understanding the prevalence of this capacity is integral to interpreting the carbon cycle because sulfate reduction is often coupled to turnover of buried organic carbon. Our findings expand the diversity of microbial groups associated with sulfur transformations in the environment and motivate revision of biogeochemical process models based on microbial community composition.
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Affiliation(s)
- Karthik Anantharaman
- Department of Earth and Planetary Science, Berkeley, CA, USA.
- Department of Bacteriology, University of Wisconsin-Madison, Madison, WI, USA.
| | - Bela Hausmann
- Division of Microbial Ecology, Department of Microbiology and Ecosystem Science, Research Network Chemistry meets Microbiology, University of Vienna, Vienna, Austria
| | - Sean P Jungbluth
- Center for Dark Energy Biosphere Investigations, University of Southern California, Los Angeles, CA, USA
- Department of Energy, Joint Genome Institute, Walnut Creek, CA, USA
| | - Rose S Kantor
- Department of Plant and Microbial Biology, University of California, Berkeley, CA, USA
| | - Adi Lavy
- Department of Earth and Planetary Science, Berkeley, CA, USA
| | - Lesley A Warren
- Department of Civil Engineering, University of Toronto, Toronto, ON, Canada
| | - Michael S Rappé
- Hawaii Institute of Marine Biology, University of Hawaii at Manoa, Kaneohe, HI, USA
| | - Michael Pester
- Department Microorganisms, Leibniz Institute DSMZ - German Collection of Microorganisms and Cell Cultures, Braunschweig, Germany
| | - Alexander Loy
- Division of Microbial Ecology, Department of Microbiology and Ecosystem Science, Research Network Chemistry meets Microbiology, University of Vienna, Vienna, Austria
| | - Brian C Thomas
- Department of Earth and Planetary Science, Berkeley, CA, USA
| | - Jillian F Banfield
- Department of Earth and Planetary Science, Berkeley, CA, USA
- Department of Environmental Science, Policy, and Management, Berkeley, CA, USA
- Earth and Environmental Sciences, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
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6
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Dale JL, Raynor MJ, Ty MC, Hadjifrangiskou M, Koehler TM. A Dual Role for the Bacillus anthracis Master Virulence Regulator AtxA: Control of Sporulation and Anthrax Toxin Production. Front Microbiol 2018; 9:482. [PMID: 29599764 PMCID: PMC5862856 DOI: 10.3389/fmicb.2018.00482] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2017] [Accepted: 02/28/2018] [Indexed: 12/02/2022] Open
Abstract
Bacillus anthracis is an endemic soil bacterium that exhibits two different lifestyles. In the soil environment, B. anthracis undergoes a cycle of saprophytic growth, sporulation, and germination. In mammalian hosts, the pathogenic lifestyle of B. anthracis is spore germination followed by vegetative cell replication, but cells do not sporulate. During infection, and in specific culture conditions, transcription of the structural genes for the anthrax toxin proteins and the biosynthetic operon for capsule synthesis is positively controlled by the regulatory protein AtxA. A critical role for the atxA gene in B. anthracis virulence has been established. Here we report an inverse relationship between toxin production and sporulation that is linked to AtxA levels. During culture in conditions favoring sporulation, B. anthracis produces little to no AtxA. When B. anthracis is cultured in conditions favoring toxin gene expression, AtxA is expressed at relatively high levels and sporulation rate and efficiency are reduced. We found that a mutation within the atxA promoter region resulting in AtxA over-expression leads to a marked sporulation defect. The sporulation phenotype of the mutant is dependent upon pXO2-0075, an atxA-regulated open reading frame located on virulence plasmid pXO2. The predicted amino acid sequence of the pXO2-0075 protein has similarity to the sensor domain of sporulation sensor histidine kinases. It was shown previously that pXO2-0075 overexpression suppresses sporulation. We have designated pXO2-0075 “skiA” for “sporulation kinase inhibitor.” Our results indicate that in addition to serving as a positive regulator of virulence gene expression, AtxA modulates B. anthracis development.
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Affiliation(s)
- Jennifer L Dale
- Department of Microbiology and Molecular Genetics, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, TX, United States.,MD Anderson Cancer Center and UTHealth Graduate School of Biomedical Sciences, The University of Texas, Houston, TX, United States
| | - Malik J Raynor
- Department of Microbiology and Molecular Genetics, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, TX, United States.,MD Anderson Cancer Center and UTHealth Graduate School of Biomedical Sciences, The University of Texas, Houston, TX, United States
| | - Maureen C Ty
- Department of Microbiology and Molecular Genetics, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Maria Hadjifrangiskou
- Department of Microbiology and Molecular Genetics, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, TX, United States.,MD Anderson Cancer Center and UTHealth Graduate School of Biomedical Sciences, The University of Texas, Houston, TX, United States
| | - Theresa M Koehler
- Department of Microbiology and Molecular Genetics, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, TX, United States.,MD Anderson Cancer Center and UTHealth Graduate School of Biomedical Sciences, The University of Texas, Houston, TX, United States
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7
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Gell DA. Structure and function of haemoglobins. Blood Cells Mol Dis 2017; 70:13-42. [PMID: 29126700 DOI: 10.1016/j.bcmd.2017.10.006] [Citation(s) in RCA: 98] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2017] [Revised: 10/29/2017] [Accepted: 10/30/2017] [Indexed: 12/18/2022]
Abstract
Haemoglobin (Hb) is widely known as the iron-containing protein in blood that is essential for O2 transport in mammals. Less widely recognised is that erythrocyte Hb belongs to a large family of Hb proteins with members distributed across all three domains of life-bacteria, archaea and eukaryotes. This review, aimed chiefly at researchers new to the field, attempts a broad overview of the diversity, and common features, in Hb structure and function. Topics include structural and functional classification of Hbs; principles of O2 binding affinity and selectivity between O2/NO/CO and other small ligands; hexacoordinate (containing bis-imidazole coordinated haem) Hbs; bacterial truncated Hbs; flavohaemoglobins; enzymatic reactions of Hbs with bioactive gases, particularly NO, and protection from nitrosative stress; and, sensor Hbs. A final section sketches the evolution of work on the structural basis for allosteric O2 binding by mammalian RBC Hb, including the development of newer kinetic models. Where possible, reference to historical works is included, in order to provide context for current advances in Hb research.
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Affiliation(s)
- David A Gell
- School of Medicine, University of Tasmania, TAS 7000, Australia.
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8
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Abstract
The stressosome is a multi-protein signal integration and transduction hub found in a wide range of bacterial species. The role that the stressosome plays in regulating the transcription of genes involved in the general stress response has been studied most extensively in the Gram-positive model organism Bacillus subtilis. The stressosome receives and relays the signal(s) that initiate a complex phosphorylation-dependent partner switching cascade, resulting in the activation of the alternative sigma factor σB. This sigma factor controls transcription of more than 150 genes involved in the general stress response. X-ray crystal structures of individual components of the stressosome and single-particle cryo-EM reconstructions of stressosome complexes, coupled with biochemical and single cell analyses, have permitted a detailed understanding of the dynamic signalling behaviour that arises from this multi-protein complex. Furthermore, bioinformatics analyses indicate that genetic modules encoding key stressosome proteins are found in a wide range of bacterial species, indicating an evolutionary advantage afforded by stressosome complexes. Interestingly, the genetic modules are associated with a variety of signalling modules encoding secondary messenger regulation systems, as well as classical two-component signal transduction systems, suggesting a diversification in function. In this chapter we review the current research into stressosome systems and discuss the functional implications of the unique structure of these signalling complexes.
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9
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Abstract
The haem-based sensors are chimeric multi-domain proteins responsible for the cellular adaptive responses to environmental changes. The signal transduction is mediated by the sensing capability of the haem-binding domain, which transmits a usable signal to the cognate transmitter domain, responsible for providing the adequate answer. Four major families of haem-based sensors can be recognized, depending on the nature of the haem-binding domain: (i) the haem-binding PAS domain, (ii) the CO-sensitive carbon monoxide oxidation activator, (iii) the haem NO-binding domain, and (iv) the globin-coupled sensors. The functional classification of the haem-binding sensors is based on the activity of the transmitter domain and, traditionally, comprises: (i) sensors with aerotactic function; (ii) sensors with gene-regulating function; and (iii) sensors with unknown function. We have implemented this classification with newly identified proteins, that is, the Streptomyces avermitilis and Frankia sp. that present a C-terminal-truncated globin fused to an N-terminal cofactor-free monooxygenase, the structural-related class of non-haem globins in Bacillus subtilis, Moorella thermoacetica, and Bacillus anthracis, and a haemerythrin-coupled diguanylate cyclase in Vibrio cholerae. This review summarizes the structures, the functions, and the structure-function relationships known to date on this broad protein family. We also propose unresolved questions and new possible research approaches.
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Vinogradov SN, Tinajero-Trejo M, Poole RK, Hoogewijs D. Bacterial and archaeal globins — A revised perspective. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2013; 1834:1789-800. [DOI: 10.1016/j.bbapap.2013.03.021] [Citation(s) in RCA: 83] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2012] [Revised: 02/12/2013] [Accepted: 03/16/2013] [Indexed: 12/17/2022]
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Martínková M, Kitanishi K, Shimizu T. Heme-based globin-coupled oxygen sensors: linking oxygen binding to functional regulation of diguanylate cyclase, histidine kinase, and methyl-accepting chemotaxis. J Biol Chem 2013; 288:27702-11. [PMID: 23928310 DOI: 10.1074/jbc.r113.473249] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
An emerging class of novel heme-based oxygen sensors containing a globin fold binds and senses environmental O2 via a heme iron complex. Structure-function relationships of oxygen sensors containing a heme-bound globin fold are different from those containing heme-bound PAS and GAF folds. It is thus worth reconsidering from an evolutionary perspective how heme-bound proteins with a globin fold similar to that of hemoglobin and myoglobin could act as O2 sensors. Here, we summarize the molecular mechanisms of heme-based oxygen sensors containing a globin fold in an effort to shed light on the O2-sensing properties and O2-stimulated catalytic enhancement observed for these proteins.
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Affiliation(s)
- Markéta Martínková
- From the Department of Biochemistry, Faculty of Science, Charles University in Prague, 128 43 Prague 2, Czech Republic
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12
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Two surfaces of a conserved interdomain linker differentially affect output from the RST sensing module of the Bacillus subtilis stressosome. J Bacteriol 2012; 194:3913-21. [PMID: 22609918 DOI: 10.1128/jb.00583-12] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The stressosome is a 1.8-MDa cytoplasmic complex that conveys environmental signals to the σ(B) stress factor of Bacillus subtilis. A functionally irreducible complex contains multiple copies of three proteins: the RsbRA coantagonist, RsbS antagonist, and RsbT serine-threonine kinase. Homologues of these proteins are coencoded in different genome contexts in diverse bacteria, forming a versatile sensing and transmission module called RST after its common constituents. However, the signaling pathway within the stressosome itself is not well defined. The N-terminal, nonheme globin domains of RsbRA project from the stressosome and are presumed to channel sensory input to the C-terminal STAS domains that form the complex core. A conserved, 13-residue α-helical linker connects these domains. We probed the in vivo role of the linker using alanine scanning mutagenesis, assaying stressosome output in B. subtilis via a σ(B)-dependent reporter fusion. Substitutions at four conserved residues increased output 4- to 30-fold in unstressed cells, whereas substitutions at four nonconserved residues significantly decreased output. The periodicity of these effects supports a model in which RsbRA functions as a dimer in vivo, with the linkers forming parallel paired helices via a conserved interface. The periodicity further suggests that the opposite, nonconserved faces make additional contacts important for efficient stressosome operation. These results establish that the linker influences stressosome output under steady-state conditions. However, the stress response phenotypes of representative linker substitutions provide less support for the notion that the N-terminal globin domain senses acute environmental challenge and transmits this information via the linker helix.
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13
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Quin MB, Berrisford JM, Newman JA, Baslé A, Lewis RJ, Marles-Wright J. The bacterial stressosome: a modular system that has been adapted to control secondary messenger signaling. Structure 2012; 20:350-63. [PMID: 22325782 DOI: 10.1016/j.str.2012.01.003] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2011] [Revised: 01/04/2012] [Accepted: 01/04/2012] [Indexed: 12/27/2022]
Abstract
The stressosome complex regulates downstream effectors in response to environmental signals. In Bacillus subtilis, it activates the alternative sigma factor σ(B), leading to the upregulation of the general stress regulon. Herein, we characterize a stressosome-regulated biochemical pathway in Moorella thermoacetica. We show that the presumed sensor, MtR, and the scaffold, MtS, form a pseudo-icosahedral structure like that observed in B. subtilis. The N-terminal domain of MtR is structurally homologous to B. subtilis RsbR, despite low sequence identity. The affinity of the switch kinase, MtT, for MtS decreases following MtS phosphorylation and not because of structural reorganization. Dephosphorylation of MtS by the PP2C type phosphatase MtX permits the switch kinase to rebind the stressosome to reset the response. We also show that MtT regulates cyclic di-GMP biosynthesis through inhibition of a GG(D/E)EF-type diguanylate cyclase, demonstrating that secondary messenger levels are regulated by the stressosome.
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Affiliation(s)
- Maureen B Quin
- Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne NE2 4HH, UK
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