Subsystem: Cell envelope-associated LytR-CpsA-Psr transcriptional attenuators
This subsystem's description is:
The LytR-CpsA-Psr family members are putative transmembrane proteins carrying a so-called LytR-CpsA-Psr domain, which is predicted to be extracellular. LytR was first described in Bacillus subtilis, where it acts as an attenuator of the expression of both itself and the divergently transcribed lytABC operon, which encodes a putative lipoprotein (LytA), an N-acetylmuramoyl-L-alanine amidase (LytC) and its modifier LytB (Lazarevic et al., 1992). CpsA is suggested to play a role in transcription activation of the capsular polysaccharide synthesis operon of Streptococcus agalactiae (Cieslewicz et al., 2001). Psr was initially proposed to be a repressor of penicillin-binding protein 5 (PBP5) synthesis in Enterococcus hirae (Massiddet al., 1996; however, see also (Sapunaric et al. 2003)). In contrast, the LytR homolog BrpA affects autolytic activity of Streptococcus mutans (Chatfield et al., 2005) and positively influences biofilm formation ability as well as acidic and oxidative stress tolerance (Wen et al., 2006). Furthermore, BrpA inactivation alters phagocytosis by human polymorphonuclear leukocytes and the outcome of bacteremia in a rat model.
All Gram-positive organisms possess LytR-CpsA-Psr proteins, except for the Mollicutes that seem to have lost this protein family in the course of diversification. In contrast, the LytR-CpsA-Psr domain was only observed in a minority of the Gram-negatives. Notably, most of the latter posses cell walls that show features of a typical Gram-positive cell wall, such as a thick, multilayered peptidoglycan, a high cross-linking extent, or polysaccharides cross-linked to the peptidoglycan (e.g. various Cyanobacteria, Chloroflexus aurantiacus, Deinococcus radiodurans, etc) (Hubscher et al., 2008)
Members of the LytR-CpsA-Psr family of cell envelope-associated attenuators are relevant for such virulence-associated functions as β-lactam resistance, biofilm formation, and stress tolerance. Although their precise function is still unknown, they are believed to play a role in ensuring cell envelope integrity (Hubscher et al., 2008)
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