Involved in the signal transduction pathway leading to the proteolytic activation of the mother cell transcription factor pro-sigma-K during sporulation. The signaling serine protease CtpB triggers pro-sigma-K processing by cleaving the pre-processed regulatory protein SpoIVFA and is necessary for the proper timing of sigma-K activation. The enzyme shows specific recognition of a C-terminal tripeptide, Xaa-Yaa-Zaa, in which Xaa is preferably Ala or Leu, Yaa is preferably Ala or Tyr, and Zaa is preferably Ala, but then cleaves at a variable distance from the C-terminus. A typical cleavage is -Ala-Ala-|-Arg-Ala-Ala-Lys-Glu-Asn-Tyr-Ala-Leu-Ala-Ala. Activated by peptide binding to the PDZ domain. Homodimer. Is expressed in both the mother cell and forespore compartments but that synthesis in the forespore is both necessary and sufficient for the proper timing of pro-sigma-K processing. Is expressed in the forespore under the control of sigma-G, and in the mother cell under the control of sigma-E. The PDZ domain functions as a gatekeeper to the protease tunnel and defines resting and active conformations of the protease. Is cleaved by SpoIVB in vitro and in vivo but this cleavage does not appear to be necessary for CtpB activation. CtpB can also cleave itself in vivo. Pro-sigma-K processing is delayed by approximately 30 minutes, and sporulation efficiency is reduced approximately two-fold. Belongs to the peptidase S41A family.