RESUMO
At the end of 1980s, regions of the polypeptide chain of bacterial flagella subunits (flagellins) responsible for different properties of these protein polymers were identified by structural studies. It was found that the N- and C-terminal regions are responsible for the polymerization properties of subunits, and the central region is responsible for antigenic properties of the flagellum. Soon after that, it was proposed to use variability of the central flagellin domain for directed modification to impart new properties to the flagellum surface. Such studies of flagella and other polymeric structures of bacterial origin thrived. However bacterial polymers have some shortcomings, mainly their instability to dissociating effects. This shortcoming is absent in archaeal flagella. A limiting factor was the lack of the three-dimensional structure of archaeal flagellins. A method was developed that allowed modifying flagella of the halophilic archaeon Halobacterium salinarum in a peptide that connects positively charged ions. Later, corresponding procedures were used that allowed preparing the anode material for a lithium-ion battery whose characteristics 4-5-fold exceeded those of batteries commonly used in industrial production. We describe other advantages of archaeal flagella over bacterial analogs when used in nanotechnology.
Assuntos
Archaea/química , Flagelos/química , Nanoestruturas/químicaRESUMO
Archaeal flagella are similar functionally to bacterial flagella, but structurally they are completely different. Helical archaeal flagellar filaments are formed of protein subunits called flagellins (archaellins). Notwithstanding progress in studies of archaeal flagella achieved in recent years, many problems in this area are still unsolved. In this review, we analyze the formation of these supramolecular structures by the example of flagellar filaments of halophilic archaea. Recent data on the structure of the flagellar filaments demonstrate that their supramolecular organization differs considerably in different haloarchaeal species.
Assuntos
Archaea/ultraestrutura , Proteínas Arqueais/química , Flagelos/ultraestrutura , Flagelina/química , Archaea/fisiologia , Proteínas Arqueais/genética , Proteínas Arqueais/metabolismo , Flagelos/fisiologia , Flagelina/genética , Flagelina/metabolismoRESUMO
Filaments of the flagellum of the halophilic archaeon Halobacterium salinarum consist of five flagellins: A1, A2, B1, B2, and B3, which are encoded by five genes localized in tandem in twoflgA and flgB operons. While the role of flagellins A1 and A2 has been determined, the role of the proteins, B operon products, is still unclear. A mutant strain of H. salinarum with deleted A and B flagellin genes (deltaflgAdeltaflgB) has been obtained for the first time. This strain has been used to create and analyze the strains carrying only individual B1 or B3 flagellin genes. Cells of the deltaflgAdeltaflgB strain were shown to have short filamentous formations, 7-8 nm thick, which we have named as X-filaments. It has been shown that X-filaments consist of a protein immunologically related to flagellins A and B. Expression of the B1 and B3 genes is suppressed in the absence of A1, A2, and B2. It has been shown that flagellins B1 and B3 cannot be substituted for flagellin B2 upon the formation of a curved hook-like structure, which serves as a connecting element between the flagellar filament and the motor axis. The multicomponent nature of flagella is discussed in the light of their possible involvement in other cell processes besides providing motility.
Assuntos
Flagelos/metabolismo , Flagelina/metabolismo , Halobacterium salinarum/metabolismo , Flagelos/genética , Flagelina/genética , Regulação Bacteriana da Expressão Gênica , Halobacterium salinarum/genética , Halobacterium salinarum/ultraestrutura , Mutação , ÓperonAssuntos
Flagelos/ultraestrutura , Halobacterium salinarum/ultraestrutura , Flagelos/química , Flagelos/genética , Flagelina/química , Flagelina/genética , Flagelina/ultraestrutura , Halobacterium salinarum/química , Halobacterium salinarum/genética , Mutação/genética , RNA Arqueal/genética , RNA Arqueal/metabolismo , RNA Mensageiro/genética , RNA Mensageiro/metabolismoRESUMO
Haloarchaeal flagella are composed of a number of distinct flagellin proteins, specified by genes in two separate operons (A and B). The roles of these flagellins were assessed by studying mutants of H. salinarum with insertions in either the A or the B operon. Cells of the flgA- mutant produced abnormally short, curved flagella that were distributed all over the cell surface. The flgA2- strain produced straight flagella, mainly found at the poles. The flgB- mutant had flagella of the same size and spiral shape as wild-type cells, but these cells also showed unusual outgrowths, which appeared to be sacs filled with basal body-like structures. In broth cultures of this mutant, the medium accumulated flagella with basal body-like structures at their ends.
Assuntos
Flagelina/metabolismo , Halobacterium/genética , Sequência de Bases , Primers do DNA , Flagelina/genética , Genes Arqueais , Halobacterium/ultraestrutura , Microscopia Eletrônica , Mutagênese , Óperon , PlasmídeosRESUMO
An ATP-binding protein from the haloalkaliphilic archaeon Natronobacterium magadii was purified and characterized by affinity chromatography on ATP-agarose and by fast protein liquid chromatography (FPLC) on a Mono Q column. The N-terminal 20 amino acid sequence of the kinase showed a strong sequence similarity of this protein with nucleoside diphosphate (NDP) kinases from different organisms and, accordingly, we believe that this protein is a nucleoside diphosphate kinase, an enzyme whose main function is to exchange gamma-phosphates between nucleoside triphosphates and diphosphates. Comparison of the molecular weights of the NDP kinase monomer determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) (23,000) and of the oligomer determined by sedimentation equilibrium experiments (125,000) indicated that the oligomer is a hexamer. The enzyme was autophosphorylated in the presence of [gamma-32P]ATP, and Mg2+ was required for the incorporation of phosphate. The kinase preserved the ability to transfer gamma-phosphate from ATP to GDP in the range of NaCl concentration from 90 mM to 3.5 M and in the range of pH from 5 to 12. It was found and confirmed by Western blotting that this kinase is one of the proteins that bind specifically to natronobacterial flagellins. NDP kinase from haloalkaliphiles appeared to be simple to purify and to be a suitable enzyme for studies of structure and stability compared with NDP kinases from mesophilic organisms.
Assuntos
Natronobacterium/enzimologia , Núcleosídeo-Difosfato Quinase/isolamento & purificação , Sequência de Aminoácidos , Animais , Meio Ambiente , Humanos , Concentração de Íons de Hidrogênio , Dados de Sequência Molecular , Peso Molecular , Natronobacterium/genética , Núcleosídeo-Difosfato Quinase/genética , Núcleosídeo-Difosfato Quinase/metabolismo , Conformação Proteica , Homologia de Sequência de Aminoácidos , Cloreto de SódioRESUMO
The protein compositions of archaebacteria (Halobacterium salinarium, Halobacterium volcanii, Halobacterium saccharovorum and Natronobacterium pharaonis 12) flagella have been studied. It was found that flagella of these archaebacterial species are made up of flagellins. The flagellins of H. salinarium, H. volcanii and H. saccharovorum are glycosylated. Based on the known primary sequences of Halobacterium halobium R1M1 flagellin genes, oligonucleotides to the 5'- and 3'-ends of locus A containing two out of five such genes have been synthesized. The amplified by primers fragment of chromosomal DNA coding for H. halobium flagellins A1 and A2 was used as a probe for detecting homologous sites in archaebacterial DNA. Southern blotting hybridization revealed that the DNA of all archaebacterial species tested in this study contains sequences that are homologous to genes flg A1 and flg A2 of H. halobium.
Assuntos
Archaea/metabolismo , Flagelos/metabolismo , Archaea/genética , Archaea/ultraestrutura , Sequência de Bases , Southern Blotting , Primers do DNA , Sondas de DNA , DNA Bacteriano , Flagelos/genética , Flagelina/genética , Flagelina/metabolismo , Microscopia Eletrônica , Dados de Sequência MolecularRESUMO
The structure of Halobacterium halobium R1M1 flagella is investigated by the methods of scanning microcalorimetry, circular dichroism, and electron microscopy. It is shown that melting curves of flagella in solutions with a different concentration of NaCl display only one peak of heat capacity that corresponds to one cooperatively melting domain. It is found that flagella do not dissociate after melting. The possible structural organization of archaebacterial flagella is discussed.
Assuntos
Flagelos/química , Flagelina/química , Halobacterium salinarum/química , Dobramento de Proteína , Sequência de Aminoácidos , Dados de Sequência Molecular , Estrutura Secundária de Proteína , Estrutura Terciária de ProteínaRESUMO
The fliC gene of the E. coli B38 flagellin has been cloned and its nucleotide sequence determined using the terminator method. According to the sequencing data, the flagellin contains 565 amino acid residues which exceeds by 65 residues the number of amino acid residues in the earlier decoded E. coli K12 flagellin. Strong homology was observed in the two flagellins among the 160 initial and 89 tail-ended residues, whereas the central, variable parts showed no homology. Similar to the K12 flagellin, the B38 flagellin has no serines, cysteines or tryptophans. The variable part of the fliC E. coli B38 gene contains a Chi-site which initiates the genetic recombination in E. coli and related species.
Assuntos
Escherichia coli/genética , Flagelina/genética , Sequência de Aminoácidos , Sequência de Bases , Clonagem Molecular , DNA Bacteriano , Dados de Sequência Molecular , Recombinação Genética , Homologia de Sequência de AminoácidosRESUMO
A model of tertiary and quaternary structure of E. coli flagellin is suggested. According to this model, the molecule consists of two independent parts. One of them is formed by the N- and C-terminal regions of the polypeptide chain and is responsible for polymerization properties. The other consists of the central region of the polypeptide chain and composes that part of the molecular globule that forms the flagella surface. It is suggested that different artificial supramolecular structures can be constructed from flagellin molecules by varying the surface domain, i.e. the central part of the polypeptide chain, and by using the domain responsible for polymerization properties as a universal block for assembly. The simplest possible artificial supramolecular structures that can be constructed from flagellins of different strains are discussed.
Assuntos
Proteínas de Bactérias , Escherichia coli , Flagelina , Modelos Moleculares , Sequência de Aminoácidos , Substâncias Macromoleculares , Dados de Sequência Molecular , Conformação ProteicaRESUMO
Flagellins of two Escherichia coli strains and their tryptic fragments were studied by different methods. Probabilities of secondary structure formation were also calculated for all flagellins with a known primary structure. The obtained data permit one to suggest a model for the flagellin molecule consisting of a central part responsible for antigenic properties and terminals responsible for polymerization. The central part is variable in length from a few amino acid residues to three-four hundred depending on the bacterial species. The terminal parts consist of about 160 amino acid residues from the N-end and 100 from the C-end.
Assuntos
Proteínas de Bactérias , Escherichia coli/análise , Flagelina , Proteínas de Bactérias/metabolismo , Flagelina/metabolismo , Imunodifusão , Substâncias Macromoleculares , Fragmentos de Peptídeos/análise , Conformação Proteica , TripsinaRESUMO
Flagellins of two Escherichia coli strains have been investigated by limited proteolysis and scanning microcalorimetry. It has been shown that a monomer flagellin consists of two parts: a central one cooperatively melting, rather resistant to proteases, and the other without a stable tertiary structure and thus easily degrading terminals. Just these terminals acquire a regular structure during polymerization. Core fragments of the two strains have been isolated and characterized.
Assuntos
Proteínas de Bactérias , Escherichia coli/metabolismo , Flagelina , Proteínas de Bactérias/metabolismo , Quimotripsina , Brometo de Cianogênio , Flagelina/metabolismo , Substâncias Macromoleculares , Peso Molecular , Fragmentos de Peptídeos/análise , Termodinâmica , Termolisina , TripsinaRESUMO
The chemotaxis of bacteria such as Salmonella and Escherichia coli involves smooth swimming punctuated by periods of tumbling. In smooth swimming the flagellar filaments are left-handed, in tumbling they are right-handed with a different wavelength. The filaments are constructed from a globular protein, flagellin, by a process of self-assembly. The existing models assume that the flagellin molecule is bistable and longitudinal rows of subunits take one of the two possible conformations. Such a model explains the observed different morphology of the flagellum. We have studied Salmonella and E. coli flagellins in polymeric and monomeric forms by scanning microcalorimetry and circular dichroism. We have inferred that a flagellin molecule consists of several domains, two of which are structured at physiological temperatures and are in the monomeric form, while the others acquire a regular form only in the process of polymerization. This phenomenon may be the basis of a process during which the flagellin molecule, fitting into the flagellum, acquires a conformation analogous to that of the neighbouring molecule in the longitudinal row.
Assuntos
Proteínas de Bactérias/isolamento & purificação , Escherichia coli/fisiologia , Flagelina/isolamento & purificação , Salmonella/fisiologia , Movimento Celular , Quimiotaxia , Flagelos/fisiologia , Cinética , Desnaturação Proteica , TermodinâmicaRESUMO
Scanning microcalorimetric and circular dichroism studies of the normal and mutant flagellins of Salmonella suggest that they have a multidomain structure in common. Flagellin polymers (flagella) are depolymerized irreversibly into monomers as the temperature is raised, and the monomers undergo denaturation reversibly when cooled and heated again. The calorimetric enthalpy of this reversible process is twice as large as the van't Hoff enthalpy, suggesting that flagellin monomers contain two co-operative regions that melt independently at the same temperature. In all flagellin specimens examined, the ellipticity at the same temperature. In all flagellin specimens examined, the ellipticity at 222 nm of polymers at room temperature is 1.6 times as large as that of monomers, and the dependence of ellipticity on temperature takes place in the same temperature intervals in which calorimetric effects take place. From these results, we propose that flagellin molecules consist of several domains, two of which are distinctly structured in monomers at room temperature, while the others acquire more regular structures during polymerization.