TCDB is operated by the Saier Lab Bioinformatics Group

9.B.157 The Cell Shape-determining MreBCD (MreBCD) Family 

The minCD/mreBCD genes together comprise an operon (Levin et al. 1992).The MreB (also called FtsA) proteins of Escherichia coli, Bacillus subtilis and Caulobacter crescentus form actin-like cables lying beneath the cell surface (Soufo and Graumann 2003). These MreB proteins are homologous to Hsp70 chaparone proteins (TC# 1.A.33) and distantly related to exopolyphosphatases andPpx/GppA family phosphatases. The cables are required to guide longitudinal cell wall synthesis, and their absence leads to merodiploid spherical and inflated cells prone to cell lysis. In B. subtilis, E. coli and C. crescentus, the mreB gene is essential. E. coli cells depleted of mreBCD became spherical, enlarged and finally lyse. Depletion of each mre gene separately conferred similar gross changes in cell morphology and viability. Thus, the three proteins encoded by mreBCD are all essential and function in the same morphogenetic pathway.

Interestingly, the presence of a multicopy plasmid carrying the ftsQAZ genes suppressed the lethality of deletions in the mre operon (Kruse et al. 2005). The MreC and MreD proteins associate with the cell membrane, and MreC interacts with both MreB and MreD. Thus, the E. coli MreBCD complex forms an essential membrane-bound complex. While MreB has 0 TMSs, MreC has 1 N-terminal TMS, and MreD has 5 or 6 TMSs. It has been proposed that the membrane-associated MreBCD complex directs longitudinal cell wall synthesis in a process essential to maintain cell morphology (Kruse et al. 2005).  The Bacillus halodurans MreD is similar in sequence to members of ABC sub-family 3.A.1.26 in TCDB, warranting inclusion of MreBCD in TCDB.  No direct evidence implicates MreD in transport.

References associated with 9.B.157 family:

Kruse, T., J. Bork-Jensen, and K. Gerdes. (2005). The morphogenetic MreBCD proteins of Escherichia coli form an essential membrane-bound complex. Mol. Microbiol. 55: 78-89. 15612918
Levin, P.A., P.S. Margolis, P. Setlow, R. Losick, and D. Sun. (1992). Identification of Bacillus subtilis genes for septum placement and shape determination. J. Bacteriol. 174: 6717-6728. 1400224
Sigle, S., N. Ladwig, W. Wohlleben, and G. Muth. (2015). Synthesis of the spore envelope in the developmental life cycle of Streptomyces coelicolor. Int. J. Med. Microbiol. 305: 183-189. 25595023
Soufo, H.J. and P.L. Graumann. (2003). Actin-like proteins MreB and Mbl from Bacillus subtilis are required for bipolar positioning of replication origins. Curr. Biol. 13: 1916-1920. 14588250
Vollmer, B., N. Steblau, N. Ladwig, C. Mayer, B. Macek, L. Mitousis, S. Sigle, A. Walter, W. Wohlleben, and G. Muth. (2019). Role of the Streptomyces spore wall synthesizing complex SSSC in differentiation of Streptomyces coelicolor A3(2). Int. J. Med. Microbiol. 309: 151327. 31324525