The role and regulation of the extracellular proteases of Staphylococcus aureus.
Staphylococcus aureus has several extracellular proteases with proposed roles in virulence. SspA (serine protease), SspB (cysteine protease) and Aur (metalloprotease) have been characterized previously and SspA and SspB were found to be cotranscribed. The coding region for the cysteine protease ScpA has been identified and characterized. It is in a probable bi-cistronic operon with scpA located immediately upstream of a coding region for a 108 aa protein that is a specific inhibitor of ScpA. Using primer extension analysis promoters have been mapped and it was found that sigmaA is the only sigma factor involved in the transcription of scpA, sspABC and aur. The transcription of all the genes occurs maximally at post-exponential phase, being positively regulated by agr (accessory gene regulator) and negatively regulated by sarA (staphylococcal accessory regulator). Furthermore sigmaB represses transcription from the aur and scp operons similarly to the previously shown effect on ssp [Horsburgh, M., Aish, J., White, I., Shaw, L., Lithgow, J. & Foster, S. (2002). J Bacteriol 184, 5457-5467]. Using mutations in each protease gene the proteolytic cascade of activation has been analysed. Aur, SspA, SspB and ScpA are all produced as zymogens, activated by proteolytic cleavage. Although the metalloprotease, Aur, does catalyse activation of the SspA zymogen, it is not the sole agent capable of conducting this process. Site-directed mutagenesis revealed that Aur is not capable of undergoing auto-proteolysis to achieve activation. The cysteine protease, ScpA, appears to reside outside this cascade of activation, as mature ScpA was observed in the aur, sspA and sspB mutant strains. Using a mouse abscess model, it has been shown that insertional inactivation of sspA or sspB results in significant attenuation of virulence, whilst mutations in aur or scpA do not. It is likely the attenuation observed in the sspA strain is due to polarity on the sspB gene.
Shaw
Lindsey
L
Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, UK.
Golonka
Ewa
E
Department of Microbiology, Faculty of Biotechnology, Jagiellonian University, 7 Gronostajowa St, 30-387 Kraków, Poland.
Potempa
Jan
J
Department of Microbiology, Faculty of Biotechnology, Jagiellonian University, 7 Gronostajowa St, 30-387 Kraków, Poland.
Foster
Simon J
SJ
Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, UK.
D000818:Animals; D001483:Base Sequence; D002874:Chromosome Mapping; D004269:DNA, Bacterial / Q000235:genetics; D010450:Endopeptidases / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000235:genetics / Q000378:metabolism; D045604:Extracellular Fluid / Q000201:enzymology; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009876:Operon; D011401:Promoter Regions, Genetic; D013203:Staphylococcal Infections / Q000209:etiology; D013211:Staphylococcus aureus / Q000201:enzymology* / Q000235:genetics / Q000472:pathogenicity; D014774:Virulence / Q000235:genetics / Q000502:physiology
D004269:DNA, Bacterial; D004792:Enzyme Precursors; D010450:Endopeptidases