MreB

MreB is a bacterial actin homolog that plays a central role in determining and maintaining cell shape in many rod- and some spiral-shaped bacteria. It is a cytoskeletal protein that polymerizes into filaments located just under the cytoplasmic membrane and forms dynamic structures that can run along the length of the cell or around its circumference.

Function and interactions: MreB organizes the synthesis of peptidoglycan, guiding where new cell wall material is inserted during growth. This activity helps maintain a rod-like morphology rather than a spherical shape. MreB interacts with several membrane-associated proteins, including MreC, MreD, and RodZ, which help anchor MreB to the inner membrane and coordinate wall synthesis with cell elongation.

Localization and dynamics: In many bacteria, MreB filaments appear as patches or helical filaments that exhibit dynamic movement within the cell cortex, a behavior linked to the regulated delivery of cell-wall precursors. The polymerization and turnover of MreB are generally dependent on nucleotide binding and hydrolysis, resembling the behavior of actin in eukaryotes.

Genetic and phenotypic effects: Disruption of MreB function often leads to loss of rod shape, producing near-spherical or irregular cells and slowed growth in various species such as Escherichia coli and Bacillus subtilis. The degree of reliance on MreB can vary among bacteria, reflecting diversity in cell-shape control mechanisms.

Regulation and research tools: The small molecule A22 inhibits MreB polymerization and is used to study its role in cell shape. MreB is a member of the broader actin superfamily and is part of a larger network of cytoskeletal elements that contribute to bacterial cell organization, alongside partners like FtsZ and, in some species, crescentin.