The C-terminal processing protease, CtpB (YvjB). Crystal structures reflecting distinct functional states show that CtpB constitutes a ring-like protein scaffold penetrated by two narrow tunnels. Access to the proteolytic sites sequestered within these tunnels is controlled by PDZ domains that rearrange upon substrate binding. Accordingly, CtpB resembles a minimal version of a self-compartmentalizing protease regulated by a unique allosteric mechanism (Mastny et al. 2013).  May show limited sequence similarity with 8.A.24.1.1.  The transmembrane domain serves as a receptor for the LsbB bacteriocin in Lactococcus lactis (Miljkovic et al. 2016).