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Using the example of a number of representatives of bacteria and archaea, the structure of their cell surface biopolymers is considered, taking into account post-translational modifications of proteins and contemporary views on the features of protein folding.

It was shown that the Haloferax volcanii flagella assembly system can accept alien flagellins and build functional recombinant flagella. The results can be used for targeted flagella modification to create multifunctional nanomaterials.

Halophilic archaea from the genus Halorubrum possess two extraordinarily diverged archaellin genes, flaB1 and flaB2. To clarify roles for each archaellin, we compared two natural Halorubrum lacusprofundi strains: One of them contains both archaellin genes, and the other has the flaB2 gene only. Both strains synthesize functional archaella; however, the strain, where both archaellins are present, is more motile. In addition, we expressed these archaellins in a Haloferax volcanii strain from which the endogenous archaellin genes were deleted. Three Hfx. volcanii strains expressing Hrr. lacusprofundi archaellins produced functional filaments consisting of only one (FlaB1 or FlaB2) or both (FlaB1/FlaB2) archaellins. All three strains were motile, although there were profound differences in the efficiency of motility. Both native and recombinant FlaB1/FlaB2 filaments have greater thermal stability and resistance to low salinity stress than single‐component filaments. Functional supercoiled Hrr. lacusprofundi archaella can be composed of either single archaellin: FlaB2 or FlaB1; however, the two divergent archaellin subunits provide additional stabilization to the archaellum structure and thus adaptation to a wider range of external conditions. Comparative genomic analysis suggests that the described combination of divergent archaellins is not restricted to Hrr. lacusprofundi, but is occurring also in organisms from other haloarchaeal genera., The significance of archaellin multiplicity remains unclear. We compared two Halorubrum lacusprofundi strains, one of them has two extraordinarily diverged archaellin genes, while another one has only one gene. In addition we engineered Haloferax volcanii strains synthesizing recombinant archaella of Hrr. lacusprofundi archaellins. The results suggest that functional supercoiled archaella can be composed from only one archaellin. However, interaction of two different archaellins provides additional stabilization to the archaellum structure and thus adaptation to a wider range of environments.

Microorganisms require a motility structure to move towards optimal growth conditions. The motility structure from archaea, the archaellum, is fundamentally different from its bacterial counterpart, the flagellum, and is assembled in a similar fashion as type IV pili. The archaellum filament consists of thousands of copies of N‐terminally processed archaellin proteins. Several archaea, such as the euryarchaeon Haloarcula marismortui, encode multiple archaellins. Two archaellins of H. marismortui display differential stability under various ionic strengths. This suggests that these proteins behave as ecoparalogs and perform the same function under different environmental conditions. Here, we explored this intriguing system to study the differential regulation of these ecoparalogous archaellins by monitoring their transcription, translation, and assembly into filaments. The salt concentration of the growth medium induced differential expression of the two archaellins. In addition, this analysis indicated that archaellation in H. marismortui is majorly regulated on the level of secretion, by a still unknown mechanism. These findings indicate that in archaea, multiple encoded archaellins are not completely redundant, but in fact can display subtle functional differences, which enable cells to cope with varying environmental conditions.

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.

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.

In the current study, haloarchaea Halobacterium salinarum cells were transformed individually with each of the modified archaellin genes (flaA1, flaA2 and flaB2) containing an oligonucleotide insert encoding the FLAG peptide (DYKDDDDK). The insertion site was selected to expose the FLAG peptide on the archaella filament surface. Three types of transformed cells synthesizing archaella, containing A1, A2, or B2 archaellin modified with FLAG peptide were obtained. Electron microscopy of archaella has demonstrated that in each case the FLAG peptide is available for the specific antibody binding. It was shown for the first time that the B2 archaellin, like archaellins A1 and A2, is found along the whole filament length.

Modified flagella of halophilic archaea Halobacterium salinarum mineralized by cobalt oxide and applied to a conductive nickel grid support have been tested as a material for the negative electrode of a lithium-ion battery. It is found that the reversible capacity of such nanostructured samples exceeded 400 mAh/g and their stability in cycling increased significantly when flagella were fragmented by sonication prior to mineralization with cobalt oxide.

Archaeal flagella are among the most perspective biopolymer structures for use in nanotechnology and have certain advantages over both bacterial analogues and viral particles. Such advantages include their resistance to dissociating agents and their adhesion properties to certain types of surfaces. As a rule, archaeal flagella consist of several protein subunit types (flagellins). This allows multifunctional filaments to be designed with each flagellin differently modified. One of the reasons that archaeal flagella have not been used in nanotechnology is the lack of data about the spatial structure of subunits in flagella. We present an experimental approach for determining flagellin molecule sites which are exposed on the flagellum surface and suitable for directed insertion of groups capable of binding certain ligands. It was shown that modified flagella of halophilic archaea Halobacterium salinarum can be used as scaffolds for designing nowel nanomaterials.

Many Archaea use rotation of helical flagellar filaments for swimming motility. We isolated and characterized the flagellar filaments of Haloarcula marismortui , an archaeal species previously considered to be nonmotile. Two Haloarcula marismortui phenotypes were discriminated—their filaments are composed predominantly of either FlaB or FlaA2 flagellin, and the corresponding genes are located on different replicons. FlaB and FlaA2 filaments differ in antigenicity and thermostability. FlaA2 filaments are distinctly thicker (20–22 nm) than FlaB filaments (16–18 nm). The observed filaments are nearly twice as thick as those of other characterized euryarchaeal filaments. The results suggest that the helicity of Haloarcula marismortui filaments is provided by a mechanism different from that in the related haloarchaeon Halobacterium salinarum , where 2 different flagellin molecules present in comparable quantities are required to form a helical filament.

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 two flgA 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 (ΔflgAΔflgB) 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 ΔflgAΔflgB 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.

Designing a new generation of energy-intensive and sustainable electrode materials for batteries to power a variety of applications is an imperative task. The use of biomaterials as a nanosized structural template for these materials has the potential to produce hitherto unachievable structures. In this report, we have used genetically modified flagellar filaments of the extremely halophilic archaea species Halobacterium salinarum to synthesize nanostructured iron oxide composites for use as a lithium-ion battery anode. The electrode demonstrated a superior electrochemical performance compared to existing literature results, with good capacity retention of 1032 mAh g(-1) after 50 cycles and with high rate capability, delivering 770 mAh g(-1) at 5 A g(-1) (similar to 5 C) discharge rate. This unique flagellar filament based template has the potential to provide access to other highly structured advanced energy materials in the future.

We have determined the nucleotide sequence of a flagellin gene locus from the haloalkaliphilic archaeon Natrialba magadii , identified the gene products among proteins forming flagella, and demonstrated cotranscription of the genes. Based on the sequence analysis we suggest that different regions of the genes might have distinct evolutionary histories including possible genetic exchange with bacterial flagellin genes.

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.

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.

Angiogenin is a potent stimulator of angiogenesis. It interacts with endothelial cells and induces a wide range of cellular responses initiating a process of blood vessel formation. One important target of angiogenin is endothelial cell-surface actin, and their interaction might be one of crucial steps in angiogenin-induced neovascularization. Recently, it was shown that angiogenin inhibits polymerization of G-actin and changes the physical properties of F-actin. These observations suggest that angiogenin may cause changes in the cell cytoskeleton. This chapter reviews the current state of the literature regarding angiogenin structure and function and discusses the relationship between the angiogenin and actin and possible functional roles of their interaction.

Angiogenin is a potent inducer of angiogenesis, a process of blood vessel formation. It interacts with endothelial and other cells and elicits a wide range of cellular responses including migration, proliferation, and tube formation. One important target of angiogenin is endothelial cell-surface actin and their interaction might be one of essential steps in angiogenin-induced neovascularization. Based on earlier indications that angiogenin promotes actin polymerization, we studied the binding interactions between angiogenin and actin in a wide range of conditions. We showed that at subphysiological KCl concentrations, angiogenin does not promote, but instead inhibits polymerization by sequestering G-actin. At low KCl concentrations angiogenin induces formation of unstructured aggregates, which, as shown by NMR, may be caused by angiogenin's propensity to form oligomers. Binding of angiogenin to preformed F-actin does not cause depolymerization of actin filaments though it causes their stiffening. Binding of tropomyosin and angiogenin to F-actin is not competitive at concentrations sufficient for saturation of actin filaments. These observations suggest that angiogenin may cause changes in the cell cytoskeleton by inhibiting polymerization of G-actin and changing the physical properties of F-actin.

We examine distribution of flagellins along multicomponent flagellar filaments (FF) and protofilaments (PF) of the haloalkaliphilic archaeon Natrialba magadii using immunogold electron microscopy. A high specific polyclonal antibody raised to one of the flagellin types bound homogeneously to the undissociated FF along the full length. At the same time both uniformly labelled and completely unlabelled PF, outwardly indistinguishable one from another, were observed.

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.

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.