Archaeal Flagella as Biotemplates for Nanomaterials with New Properties.

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.

Flagella of halophilic archaea: differences in supramolecular organization.

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.

Role of flagellins from A and B loci in flagella formation of Halobacterium salinarum.

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.

Unfolding of tertiary structure of Halobacterium halobium flagellins does not result in flagella destruction.

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.

Flagellin parts acquiring a regular structure during polymerization are disposed on the molecule ends.

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.

Architectonics of a bacterial flagellin filament subunit.

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.