Figure 7

Model of the lysine- and pH-dependent activation of wild-type CadC and CadC_C208A,C272A. The different transcription activities are indicated by the arrows below CadC. Under non-inducing conditions (no lysine, pH 7.6) CadC-mediated cadBA expression is inhibited by two mechanisms, the interaction with LysP and a disulfide bond in the periplasmic domain. CadC with a disulfide bond remains inactive even when the interaction with LysP is released in the presence of lysine (lysine, pH 7.6). A shift to low pH causes conformational changes and prevents formation of a disulfide bond (lysine, pH 5.8). In the absence of lysine, CadC activity is blocked by the interplay with LysP (no lysine, pH 5.8). In CadC_C208A,C272A formation of a disulfide bond is prevented by amino acid replacements. As consequence, this derivative displays semi-active states at pH 7.6 in the presence of lysine (lysine, pH 7.6), and at pH 5.8 in the absence of lysine (no lysine, pH 5.8). See text for further details.