The actin-like MreB proteins in Bacillus subtilis a new turn

Abstract

A decade ago, two breakthrough descriptions were reported: 1) the first helix-like protein localization pattern of MreB and its paralog Mbl in Bacillus subtilis and 2) the crystal structure of Thermotoga maritima MreB1, which was remarkably similar to that of actin. These discoveries strongly stimulated the field of bacterial development, leading to the identification of many new cytoskeletal proteins (1) and the publication of many studies describing the helical patterns of protein, DNA and even lipid domains. However, today, new breakthroughs are shaking up what had become a dogma. Instead of helical structures, MreBs appear to form discrete patches that move circumferentially around the cell, questioning the idea of MreB cables forming an actin-like cytoskeleton. Furthermore, increasing evidence of biochemical properties that are unlike the properties of actin suggest that the molecular behavior of MreB proteins may be different. The aim of this review is to summarize the current knowledge of the so-called "actin-like" MreB cytoskeleton through a discussion of the model Gram-positive bacterium B. subtilis and the most recent findings in this rapidly evolving research field.

The membrane: transertion as an organizing principle in membrane heterogeneity

“…This movement of MreB did not, as one would have expected, follow a helical pattern. Recent reports and reviews suggest that the distribution pattern reported for E. coli MreB mainly resembles that reported for B. subtilis MreB: a punctuated pattern with pairs of dots or small bands generally described as helical (van Teeffelen et al, 2011; Chastanet and Carballido-Lopez, 2012; Margolin, 2012; Errington, 2015). Indeed, MreB proteins form elongated filamentous structures when over-produced or when observed in late phases of growth.…”

Hydrolysis of peptidoglycan is modulated by amidation of meso‐diaminopimelic acid and Mg2+ in Bacillus subtilis

“…However, when growth media are supplemented with 5–25 mM Mg 2+ , mreB and mbl mutants grow and divide normally and assume a normal rod‐shaped morphology. When Mg 2+ is depleted, the morphological phenotype becomes manifest and they grow as deformed and ballooning cells before eventually lysing (Formstone and Errington, 2005; Chastanet and Carballido‐Lopez, 2012). Mg 2+ likewise suppresses the viability and/or morphological defects of several other cell wall related mutants (e.g.…”

“…Mg 2+ likewise suppresses the viability and/or morphological defects of several other cell wall related mutants (e.g. mreC, mreD, ponA, ugtP, pgcA or gtaB) (Murray et al ., 1998; Chastanet and Carballido‐Lopez, 2012), but the mechanism underlying this rescuing role is currently unknown. Two main hypotheses have been put forth to explain it.…”

Peptidoglycan synthesis drives an FtsZ-treadmilling-independent step of cytokinesis

“…Therefore, different bacterial shapes are mainly determined by the spatial and temporal regulation of PG synthesis, not by its chemical composition. Rod-shaped bacteria, such as Bacillus subtilis or Escherichia coli, achieve their shape through the action of two PG synthesis machines that act at the septum and at the lateral wall, in processes coordinated by cytoskeletal proteins FtsZ and MreB, respectively 1,2 . The tubulin homologue FtsZ is the first protein recruited to the division site where it assembles in filaments (Z-ring) that undergo treadmilling and recruit later divisome proteins 3,4 .…”