Figure 4. Residues critical for FusA/E/B ternary complex.

The RRE domain of MccB (residues M₁-S₈₆, PDB entry 3H9J, blue) was aligned with FusE. Spheres indicate residues of FusE probed by mutagenesis. Mutagenesis at sites along α₃ drastically reduced binding to FusA_leader (orange). Ala-substitutions along β₂ and β₃ did not influence FusA_leader binding but did abolish leader peptide cleavage (green). The validity of these predicted protein-protein interaction sites is underscored by the fact mutagenesis elsewhere (gray) did not reduce leader peptide binding or leader peptidase activity.