Figure 9.

Interaction sites on YhcB. A, multiple sequence alignment of YhcB homologs across proteobacteria. The conserved residues are shown as a motif logo and histogram under the alignment, whereas the domain structure of Haemophilus ducreyi YhcB (Fig. 8) is shown above the alignment. The sequence is divided into six regions, v1 (N terminus) to v6 (C terminus), as indicated above the alignment. Highly conserved amino acid residues in each region were mutated as shown beneath the sequence. Each YhcB mutant (v1–v6) carries 4 to 6 substituted amino acid residues. B, bacterial two hybrid screens with YhcB mutants show the loss of specific interactions. The YhcB mutant (“variant”) v5 showed a loss of interactions with prey partners FtsI, RodZ, and YidC. The YhcB-v5 region possess several conserved residues predicted to be important for coiled-coil interactions as indicated by arrows underneath the sequence in panel A. No interactions were detected in the absence of the transmembrane (TM) region (v7). C, protein models show mutated and thus potentially interacting residues in both YhcB monomers and tetramers.