[Effect of heat shock on cells of phytopathogenic mycoplasma Acholeplasma laidlawii PG-8A].

Heat shock caused a more active formation of the "dormant" forms (minibodies), as well as increased production of extracellular membrane vesicles by Acholeplasma laidlawii PG-8A cells. Raise of the amount of the minibodies that have increased resistance to biogenic and abiogenic stress factors and pathogenicity may lead to more successful persistence of mycoplasmas in their hosts. Increased production of the extracellular membrane vesicles containing virulence factors by Acholeplasma laidlawii cells during stress may be an additional burden for the infected organism. It has been recently revealed that the vesicles of A. laidlawii contain appreciable quantities of small heat shock protein IbpA (Hsp20). In this paper, using immune-electron microscopy, have shown that at elevated temperature IbpA is associated with A. laidlawii minibodies. Perhaps, IbpA contributes to increased resistance and pathogenicity of the minibodies, keeping their proteins and polypeptides, including protein virulence factors in the folding-competent state.

[Mycoplasma heat shock proteins and their genes].

Mycoplasmas (class Mollicutes) are the most simply organized prokaryotic organisms capable to self-reproduction. They are considered as a model of "minimal" cell. Systems preserved by mycoplasmas in their reductive evolution may play a fundamental role in viability of any cell. Information on the genes encoding heat shock proteins (HSP) in completely sequenced mycoplasma genomes was summarized and systematized. An attempt was made to explain the presence or absence in mycoplasmas of important bacterial chaperones and proteases. These HSP are necessary not only for cell stress resistance, but for protein homeostasis under normal conditions. The mechanisms of regulation of transcription of corresponding genes are considered. Properties and functions of the most completely characterized mycoplasmal HSP are discussed: DnaK, DnaJ-like, GroEL/GroES, ClpB, and small heat shock proteins (sHSP).

[Localization of the division protein FtsZ in mycoplasma cells Mycoplasma hominis].

Localization of the protein FtsZ in Mycoplasma hominis cells was determined. Ultra thin sections were treated by rabbit polyclonal antibodies against FtsZ M. hominis: a conjugate of protein A with colloidal gold particles was used instead of secondary antibodies. Considerable polymorphism of cells was seen on electron microscopy pictures of M. hominis cells, which is typical for mycoplasmas. Among a wide variety of cell shapes we distinguished dumbbell-shaped dividing cells, and the cells connected with each other with the aid of thin membrane tubules (former constrictions). Dominants distribution of the label in the constriction area of dividing M. hominis cells and in the area of the thin membrane tubules was observed. We revealed the cross septum in the mycoplasma cells for the first time, as well as the gold labeling of this structure. Furthermore, in some rounded and oval cells colloidal gold particles labeled the whole plasma membrane in ring-shaped manner. Probably, the label in these cases marks a submembrane contractile ring (Z-ring). The facts mentioned above confirm that FtsZ of M. hominis plays an active role in the mycoplasma cytokinesis. In a series of cases spiral-like distribution of gold particles was observed. Probably, FtsZ protofilaments in M. hominis cells can form spiral structures similar to Z-spirals of Bacillus subtilis and Escherichia coli. Its presence in mycoplasma cells may be considered as an important argument in favour of model of Z-ring assembling through reorganization of Z-spirals. FtsZ also may participate in maintenance of mycoplasma cell shape (membrane localization).

[The heat shock protein of alpha-crystallin type from mycoplasma (Acholeplasma laidlawii)].

A considerable increase in several heat shock proteins (HSPs) amount in Acholeplasma laidlawii cells has been revealed after temperature rising of liquid culture; and the quantity of small HSP, named p17, was increased in a hundred of times. The p17 protein was isolated and identified as HSP of alpha-crystallin type (alpha-HSP). It became possible as a result of sequencing of 15 amino acids from N-terminal of the p17 polypeptide chain, followed by revealing of a corresponding open reading frame (ORF) in a completely sequenced genome of A. laidlawii PG 8A. Computer-based search for homologous ORFs in all 17 genomes of Mycoplasmataceae family (the mycoplasmas themselves) that had been completely sequenced to date, gives negative result. But among the representatives of Mollicutes (mycoplasma) class, the genes coding alpha-HSPs were found in two Phytoplasma species (Phytoplasmataceae family) and the acholeplasma examined (Acholeplasmataceae family). It supposed that presence or absence of alpha-HSPs in microorganisms might be connected with the fact that representatives of Acholeplasmataceae and Phytoplasmataceae families inhabit principally in plant tissues in contrast to majority of Mycoplasmataceae family, that inhabit animal and human tissues, i. e. use ecological niches with relatively constant temperature.

[FtsZ and the division of bacterial cell].

In this review we have tried to describe proteins and supermolecular structures which take part in the division of bacterial cell. The principal cell division protein of the most of prokaryotes is FtsZ, a homologue of eukaryotic tubulin. FtsZ just as tubulin is capable to bind and hydrolyze GTP. The division of bacterial cell begins with forming of so called divisome. The basis of such divisome is a contractile ring (Z ring); the ring encircles the cell about midcell. Z ring consists of a bundle of laterally bound protofilaments, which have been formed as a result of FtsZ polymerization. Z ring is rigidly bounded to cytozolic side of inner membrane with participation of FtsA, ZipA, FtsW and many other cell division proteins of divisome. The ring directs the process of cytokinesis transmitting power of constriction to membrane. Primary structures of members of the family of prokaryotic FtsZs differ from eukaryotic tubulines significantly except the region, where the site of GTP binding is placed. There is high degree of homology between structures of these proteins in the region. FtsZ is one of the most conservative proteins in prokaryotes, but ftsZ genes have not been found in completely sequenced genomes of several species of microorganisms. There are 2 species of mycoplasmas (Ureaplasma parvum and Mycoplasma mobile), Prostecobacter dejongeii, 10 species of chlamydia and 5 species of archaea among them. So these organisms divide without FtsZ. There are many open reading frames which encode proteins with unknown functions in genomes of U. parvum and M. mobile. The comparison of primary structures of these hypothetical proteins with structures of cell division proteins did not allow researchers to find similar proteins among them. We suppose that the process of cell division of these organisms should recruit proteins with function similar to FtsZ and having homologous with FtsZ or other cell division proteins spatial structures.