Bacterial Adaptor Membrane Fusion Proteins and the Structurally Dissimilar Outer Membrane Auxiliary Proteins Have Exchanged Central Domains in 𝛼-Proteobacteria

Figure 1

Alignment of a large portion of an OMA from Sinorhizobium meliloti (an α-proteobacterium) (top; CAC49052) with a homologous portion of an MFP from Nitrococcus mobilis (a γ-proteobacterium) (bottom; EAR21905). Only OMA homologues from ∞-proteobacteria were retrieved as top hits when this region of the OMA of S. meliloti was used as the query sequence in BLAST searches, while only MFP homologues were retrieved as top hits when this portion of the MFP of N. mobilis was used as the query sequence. All proteins retrieved in BLAST searches as top hits that were not from α-proteobacteria proved to be MFPs rather than OMAs when this region of the S. meliloti homologue was used as the query sequence. For the comparison shown, the GAP program with default settings and 500 random shuffles gave 30% identity, 41% similarity, 0% gaps, and a comparison score of 23 SD. These values are far in excess of the values needed to establish homology [3, 5, 20]. The regions of striking identity are between resides 191 and 374 in the OMA and between residues 88 and 271 in the MFP as shown. These are the 𝛼-helical regions of both proteins as indicated in Figure 3. Vertical lines, identities; double and single dots, close and distant similarities as defined by the GAP program, respectively. Numbers at the beginning and end of each line of the two aligned sequences refer to residue numbers in the proteins.