Fig. 5.

A histidine switch in RopB senses environmental pH. a Individual subunits of RopB–CTD dimer are color-coded in dark and light gray. The N- and C-termini of one subunit is marked as N and C, respectively. The two SIP-binding pockets in each subunit of a RopB–CTD dimer are circled (dotted lines). The green line connecting the two SIP-binding pockets indicates the location of the base of the SIP-binding pocket. SIP located in the peptide-binding pockets of the RopB–CTD dimer are shown as sticks and colored in cyan. The main chain atoms of surface-exposed histidines in one subunit of RopB–CTD are shown as green spheres and labeled. The side chains of H144, Y176, Y182’, and E185’ located at the base of the SIP-binding pocket for each subunit of a RopB–CTD dimer are shown as spheres and boxed in red rectangle (and in panel b). The ‘ indicates the amino acid residue from the second subunit of a RopB–CTD dimer. The side chains of the amino acid residues involved in intramolecular interactions from two subunits of a RopB–CTD dimer are color-coded in orange and purple, respectively. b A magnified view of the intramolecular interactions at the base of SIP-binding pocket of RopB in the boxed area (red) in panel a. The side chains of H144, Y176, Y182’, and E185’ located at the base of the SIP-binding pocket for each subunit of a RopB–CTD dimer are shown as sticks and the side chains from two subunits are color-coded in orange and purple, respectively. The amino acid residues from the second subunit of RopB–CTD dimer are indicated by ’. The distances (in angstroms, Å) between the amino acid residues are shown