SIGNIFICANCE

The formation and degradation of S-nitrosothiols (SNOs) are important mechanisms of post-translational protein modification and appear to be ubiquitous in biology. These processes play well-characterized roles in eukaryotic cells, including a variety of pathologies and in relation to chronic conditions. We know little of the roles of these processes in pathogenic and other bacteria.

RECENT ADVANCES

It is clear, mostly from growth and transcriptional studies, that bacteria sense and respond to exogenous SNOs. These responses are phenotypically and mechanistically distinct from the responses of bacteria to nitric oxide (NO) and NO-releasing agents, as well as peroxynitrite. Small SNOs, such as S-nitrosoglutathione (GSNO), are accumulated by bacteria with the result that intracellular S-nitrosoproteins (the 'S-nitrosoproteome') are detectable. Recently, conditions for endogenous SNO formation in enterobacteria have been described.

CRITICAL ISSUES

The propensity of intracellular proteins to form SNOs is presumably constrained by the same rules of selectivity that have been discovered in eukaryotic systems, but is also influenced by uniquely bacterial NO detoxification systems, exemplified by the flavohemoglobin Hmp in enterobacteria and NO reductase of meningococci. Furthermore, the bacterial expression of such proteins impacts upon the formation of SNOs in mammalian hosts.

FUTURE DIRECTIONS

The impairment during bacterial infections of specific SNO events in the mammalian host is of considerable interest in the context of proteins involved in innate immunity and intracellular signalling. In bacteria, numerous mechanisms of S-nitrosothiol degradation have been reported (e.g., GSNO reductase); others are thought to operate, based on consideration of their mammalian counterparts. The nitrosothiols of bacteria and particularly of pathogens warrant more intensive investigation.