Abstract
Bacteria encase their cytoplasmic membrane with peptidoglycan (PG) to maintain the shape of the cell and protect it from bursting. The enlargement of the PG layer is facilitated by the coordinated activities of PG synthesising and -cleaving enzymes. In Escherichia coli, the cytoplasmic membrane-bound lytic transglycosylase MltG associates with PG synthases and was suggested to terminate the polymerisation of PG glycan strands. Using pull-down and surface plasmon resonance, we detected interactions between MltG from Bacillus subtilis and two PG synthases; the class A PBP1 and the class B PBP2B. Using in vitro PG synthesis assays with radio-labelled or fluorophore-labelled B. subtilis-type and/or E. coli-type lipid II, we showed that both, BsMltG and EcMltG, are lytic tranglycosylases and that their activity is higher during ongoing glycan strand polymerisation. MltG competed with the transpeptidase activity of class A PBPs, but had no effect on their glycosyltransferase activity, and produced glycan strands with a length of 7 disaccharide units from cleavage in the nascent strands. We hypothesize that MltG cleaves the nascent strands to produce short glycan strands that are used in the cell for a yet unknown process.
Highlights
Most bacteria are engulfed by peptidoglycan (PG), a mesh-like molecule that maintains the shape of the cell and protects it from bursting due to the turgor (Vollmer et al, 2008)
EcMltG presumably associates with EcPBP1B based on bacterial twohybrid experiments (Yunck et al, 2016)
BsPBP1 was present in the bound fraction when applied together with His-BsMltG suggesting the two proteins interact
Summary
Most bacteria are engulfed by peptidoglycan (PG), a mesh-like molecule that maintains the shape of the cell and protects it from bursting due to the turgor (Vollmer et al, 2008). In Bacillus subtilis, BsPBP1 is the most abundant class A PBP with roles in PG synthesis during length growth and cell division (Claessen et al, 2008; Pedersen et al, 1999). Escherichia coli has two semiredundant class A PBPs, EcPBP1A and EcPBP1B, with preferential roles in elongation and cell division, respectively (Banzhaf et al, 2012; Bertsche et al, 2006; Yousif et al, 1985). The SEDS proteins BsFtsW and EcFtsW interact with their cognate class B PBP, BsPBP2B and EcPBP3, respectively, and synthesise PG in the test tube (Fraipont et al, 2011; Rohs et al, 2018; Sjodt et al, 2018; Taguchi et al, 2019)
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