The PDZ domain of the SpoIVB serine peptidase facilitates multiple functions

During spore formation in Bacillus subtilis, the SpoIVB protein is a critic al component of the sigma (K) regulatory checkpoint. SpoIVB has been shown to be a serine peptidase that is synthesized in the spore chamber and which self-cleaves, releasing active forms. These forms can signal proteolytic p rocessing of the transcription factor sigma (K) in the outer mother cell ch amber of the sporulating cell. This forms the basis of the sigma (K) checkp oint and ensures accurate sigma (K)-controlled gene expression. SpoIVB has also been shown to activate a second distinct process, termed the second fu nction, which is essential for the formation of heat-resistant spores. In a ddition to the serine peptidase domain, SpoIVB contains a PDZ domain. We ha ve altered a number of conserved residues in the PDZ domain by site-directe d mutagenesis and assayed the sporulation phenotype and signaling propertie s of mutant SpoIVB proteins. Our work has revealed that the SpoIVB PDZ doma in could be used for up to four distinct processes, (i) targeting of itself for trans proteolysis, (11) binding to the protease inhibitor BofC, (iii) signaling of pro-sigma (K) processing, and (iv) signaling of the second fun ction of SpoIVB.