Flotillin-mediated stabilization of unfolded proteins in bacterial membrane microdomains.

The function of many bacterial processes depends on the formation of functional membrane microdomains (FMMs), which resemble the lipid rafts of eukaryotic cells. However, the mechanism and the biological function of these membrane microdomains remain unclear. Here, we show that FMMs in the pathogen methicillin-resistant Staphylococcus aureus (MRSA) are dedicated to confining and stabilizing proteins unfolded due to cellular stress.

Roles of the Essential Protein FtsA in Cell Growth and Division in Streptococcus pneumoniae.

is an ovoid-shaped Gram-positive bacterium that grows by carrying out peripheral and septal peptidoglycan (PG) synthesis, analogous to model bacilli, such as and In the model bacilli, FtsZ and FtsA proteins assemble into a ring at midcell and are dedicated to septal PG synthesis but not peripheral PG synthesis; hence, inactivation of FtsZ or FtsA results in long filamentous cells unable to divide. Here, we demonstrate that FtsA and FtsZ colocalize at midcell in and that partial depletion of FtsA perturbs septum synthesis, resulting in elongated cells with multiple FtsZ rings that fail to complete septation. Unexpectedly, complete depletion of FtsA resulted in the delocalization of FtsZ rings and ultimately cell ballooning and lysis.

The Cell Division Protein FtsZ from Streptococcus pneumoniae Exhibits a GTPase Activity Delay.

The cell division protein FtsZ assembles in vitro by a mechanism of cooperative association dependent on GTP, monovalent cations, and Mg(2+). We have analyzed the GTPase activity and assembly dynamics of Streptococcus pneumoniae FtsZ (SpnFtsZ). SpnFtsZ assembled in an apparently cooperative process, with a higher critical concentration than values reported for other FtsZ proteins.

Role of the FtsA C terminus as a switch for polymerization and membrane association.

Unlabelled: Together with ATP, the C-terminal region of the essential streptococcal FtsA protein acts as an intramolecular switch to promote its polymerization and attachment to the membrane. During septation, FtsA is known to anchor the constricting FtsZ ring and, subsequently, the divisome to the membrane. Truncation of the C terminus of the streptococcal FtsA (FtsAΔCt) facilitates a more rapid ATP-dependent polymerization in solution than is seen with the full-length protein (FtsA(+)).

Polymorphism of FtsZ filaments on lipid surfaces: role of monomer orientation.

FtsZ is a bacterial cytoskeletal protein involved in cell division. It forms a ringlike structure that attaches to the membrane to complete bacterial division. It binds and hydrolyzes GTP, assembling into polymers in a GTP-dependent manner.

In the beginning, Escherichia coli assembled the proto-ring: an initial phase of division.

Cell division in Escherichia coli begins by assembling three proteins, FtsZ, FtsA, and ZipA, to form a proto-ring at midcell. These proteins nucleate an assembly of at least 35 components, the divisome. The structuring of FtsZ to form a ring and the processes that effect constriction have been explained by alternative but not mutually exclusive mechanisms.

Key role of two terminal domains in the bidirectional polymerization of FtsA protein.

The effect of two different truncations involving either the 1C domain or the simultaneous absence of the S12-13 β-strands of the FtsA protein from Streptococcus pneumoniae, located at opposite terminal sides in the molecular structure, suggests that they are essential for ATP-dependent polymerization. These two truncated proteins are not able to polymerize themselves but can be incorporated to some extent into the FtsA(+) polymers during the assembling process. Consequently, they block the growth of the FtsA(+) polymers and slow down the polymerization rate.

Role of Escherichia coli FtsN protein in the assembly and stability of the cell division ring.

Deprivation of FtsN, the last protein in the hierarchy of divisome assembly, causes the disassembly of other elements from the division ring, even extending to already assembled proto-ring proteins. Therefore the stability and function of the divisome to produce rings active in septation is not guaranteed until FtsN is recruited. Disassembly follows an inverse sequential pathway relative to assembly.

Structural and functional model for ionic (K(+)/Na(+)) and pH dependence of GTPase activity and polymerization of FtsZ, the prokaryotic ortholog of tubulin.

Bacterial cell division occurs through the formation of a protein ring (division ring) at the site of division, with FtsZ being its main component in most bacteria. FtsZ is the prokaryotic ortholog of eukaryotic tubulin; it shares GTPase activity properties and the ability to polymerize in vitro. To study the mechanism of action of FtsZ, we used molecular dynamics simulations of the behavior of the FtsZ dimer in the presence of GTP-Mg(2+) and monovalent cations.

The order of the ring: assembly of Escherichia coli cell division components.

Topological cues appear to override temporal events in the assembly of the Escherichia coli cell division ring. When a procedure that allows the recruitment of ring components based on their topological properties is used, a concerted mode of assembly of several components of the divisome, rather than a strict linear mode, is revealed. Three multimolecular complexes, the proto-ring, the periplasmic connector and the peptidoglycan factory, show some degree of concertation for their assembly.

Cell division in cocci: localization and properties of the Streptococcus pneumoniae FtsA protein.

We studied the cytological and biochemical properties of the FtsA protein of Streptococcus pneumoniae. FtsA is a widespread bacterial cell division protein that belongs to the actin superfamily. In Escherichia coli and Bacillus subtilis, FtsA localizes to the septal ring after FtsZ, but its exact role in septation is not known.

Role of two essential domains of Escherichia coli FtsA in localization and progression of the division ring.

The FtsA protein is a member of the actin superfamily that localizes to the bacterial septal ring during cell division. Deletions of domain 1C or the S12 and S13 beta-strands in domain 2B of the Escherichia coli FtsA, previously postulated to be involved in dimerization, result in partially active proteins that do not allow the normal progression of septation. The truncated FtsA protein lacking domain 1C (FtsADelta1C) localizes in correctly placed division rings, together with FtsZ and ZipA, but does not interact with other FtsA molecules in the yeast two-hybrid assay, and fails to recruit FtsQ and FtsN into the division ring.

The heat shock proteins, Hsp70 and Hsp83, of Leishmania infantum are mitogens for mouse B cells.

Extending earlier studies, this report demonstrates that Leishmania infantum heat shock proteins (Hsps), Hsp70 and Hsp83, expressed as recombinant proteins fused to the Escherichia coil maltose-binding protein (MBP), are potent mitogens for murine splenocytes. The response was not due to lipopolysaccharide (LPS) because the stimulatory activity of Hsp preparations was sensitive to boiling and trypsin treatments, whereas the corresponding activity of LPS was resistant to both treatments. It was found that in vitro incubation of spleen cells with the Leishmania Hsps leads to the expansion of CD220-bearing populations, suggesting a direct effect of these proteins on B lymphocytes.