Anti-sigma factor YlaD regulates transcriptional activity of sigma factor YlaC and sporulation via manganese-dependent redox-sensing molecular switch in Bacillus subtilis

Abstract

YlaD, a membrane-anchored anti-sigma (sigma) factor of Bacillus subtilis, contains a HX3CXXC motif that functions as a redox-sensing domain and belongs to one of the zinc (Zn)-co-ordinated anti-sigma factor families. Despite previously showing that the YlaC transcription is controlled by YlaD, experimental evidence of how the YlaC-YlaD interaction is affected by active cysteines and/or metal ions is lacking. Here, we showed that the P-yla promoter is autoregulated solely by YlaC. Moreover, reduced YlaD contained Zn and iron, while oxidized YlaD did not. Cysteine substitution in YlaD led to changes in its secondary structure; Cys3 had important structural functions in YlaD, and its mutation caused dissociation from YlaC, indicating the essential requirement of a HX3CXXC motif for regulating interactions of YlaC with YlaD. Analyses of the far-UV CD spectrum and metal content revealed that the addition of Mn ions to Zn-YlaD changed its secondary structure and that iron was substituted for manganese (Mn). The ylaC gene expression using beta Glu activity from P-yla:gusA was observed at the late-exponential and early-stationary phase, and the ylaC-overexpressing mutant constitutively expressed gene transcripts of clpP and sigH, an important alternative s factor regulated by ClpXP. Collectively, our data demonstrated that YlaD senses redox changes and elicits increase in Mn ion concentrations and that, in turn, YlaD-mediated transcriptional activity of YlaC regulates sporulation initiation under oxidative stress and Mn-substituted conditions by regulating clpP gene transcripts. This is the first report of the involvement of oxidative stress-responsive B. subtilis extracytoplasmic function s factors during sporulation via a Mn-dependent redox-sensing molecular switch.