The Actin-like MreB 'Cytoskeleton'
from: Bacillus: Cellular and Molecular Biology (Third edition) (Edited by: Peter L. Graumann). Caister Academic Press, U.K. (2017) Pages: 223-262.
Prokaryotic cells possess filamentous proteins, analogous to eukaryotic cytoskeletal proteins, that play a key role in the spatial organization of essential cellular processes. The bacterial homologues of actin (MreB, ParM, MamK, AlfA and Alps proteins) are involved in cell shape determination, DNA segregation, cell polarity, cell motility and other functions that require the targeting and accurate positioning of proteins and molecular complexes in the cell. In Bacillus subtilis, MreB homologues (MreB, Mbl and MreBH) assemble into dynamic polymeric structures that move processively along peripheral tracks perpendicular to the cell axis together with other morphogenetic factors involved in growth of the cylindrical sidewall (elongation). The ultimate morphology of the cell is believed to depend on a dynamic interplay between the intracellular MreB proteins and the extracellular proteins that carry up cell wall biosynthesis, maturation and degradation, probably linked through MreCD and/or other membrane proteins such as RodZ. Peptidoglycan synthesis drives the circumferential movement of MreB filaments around the cell periphery, which in turn leads to spatial organization of the peptidoglycan elongation machinery. MreB isoforms of B. subtilis have also been implicated in the organization of the cell membrane and of viral DNA replication, in the inhibition of cell elongation during the escape from the competence state, and in chromosome segregation, although they do not seem to be essential for this process. The general properties of MreB proteins, relative to eukaryotic actin and to other prokaryotic homologues of actin, and the known functions of the MreB cytoskeleton in B. subtilis and other bacteria, will be discussed in this chapter read more ...