Phylogenetic analysis clearly reveals that there is a family of outer membrane proteins closely related to OprM and other outer membrane proteins implicated in efflux. Other closely related proposed outer membrane proteins (i.e. OpmN, OpmL, OpmK, OpmF, OpmH, and OpmM below) may belong to this family or another family. Notably, proteins previously shown to be involved in efflux are all within this cluster related to OprM, while proteins with similarity to OMP involved in secretion are present in the other cluster. These clusters may therefore reflect functional differences.
The above tree was constructed using
the Neighbor-joining distance matrix method. All bootstrap values for branching
order (out of a total of 100 replicates) are over 70, with the exception of
branches for OpmB, OpmK, and the cluster comprising OpmG and OpmI. Branching
order for these latter sequences can not be determined with any degree of accuracy.