Regulatory circuits controlling Spx levels in Streptococcus mutans. Issue 1 (8th April 2020)

• Record Type: Journal Article
• Authors: Ganguly, Tridib; Kajfasz, Jessica K.; Abranches, Jacqueline; Lemos, José A.
• Is Part Of: Molecular microbiology. Volume 114:Issue 1(2020)
• Page Start: 109
• Page End: 126
• Publication Date: 2020-04-08
• Subjects: ClpP -- oxidative stress -- Spx -- Streptococcus mutans; Molecular microbiology -- Periodicals; 572.829
• DOI: 10.1111/mmi.14499
• Languages: English
• ISSNs: 0950-382X

Abstract

Abstract: Spx is a major regulator of stress responses in Firmicutes. In Streptococcus mutans, two Spx homologues, SpxA1 and SpxA2, were identified as mediators of oxidative stress responses but the regulatory circuits controlling their levels and activity are presently unknown. Comparison of SpxA1 and SpxA2 protein sequences revealed differences at the C‐terminal end, with SpxA1 containing an unusual number of acidic residues. Here, we showed that a green fluorescence protein (GFP) reporter becomes unstable when fused to the last 10 amino acids of SpxA2 but remained stable when fused to the C‐terminal acidic tail of SpxA1. Inactivation of clpP or simultaneous inactivation of clpC and clpE stabilized the GFP::SpxA2tail fusion protein. Addition of acidic amino acids to the GFP::SpxA2tail chimera stabilized GFP, while deletion of the acidic residues destabilized GFP::SpxA1tail . Promoter reporter fusions revealed that spxA1 transcription is co‐repressed by the metalloregulators PerR and SloR while spxA2 transcription is largely dependent on the envelope stress regulator LiaFSR. In agreement with spxA2 being part of the LiaR regulon, SpxA2 was found to be critical for the growth of S. mutans under envelope stress conditions. Finally, we showed that redox sensing is essential for SpxA1‐dependent activation of oxidative stress responses but dispensable for SpxA2‐mediated envelope stress responses. Abstract : Streptococcus mutans encodes two Spx homologues. SpxA1 is resistant to ClpP proteolysis due to the presence of C‐terminal acidic residues, transcriptionally regulated by the metalloregulators PerR and SloR, and relies on its redox sensing motif to activate an oxidative stress response. SpxA2 levels are controlled by the LiaFSR signal transduction system and posttranslationally by ClpP proteolysis. In addition, SpxA2 was critical for the growth of S. mutans under envelope stress conditions regardless of its redox status.