MtrAB-LpqB: a conserved three-component system in actinobacteria?

Streptomyces coelicolor is the model organism for the actinobacteria, a group of high-GC Gram-positive bacteria with members that are notable both for their industrial importance as antibiotic producers and for their pathogenicity. The S. coelicolor genome encodes a subgroup of sensor kinases that is genetically linked to lipoprotein genes, at least one of which functions as an accessory protein to its co-translated kinase. Another member of this subgroup, MtrB, is widely conserved in the actinobacteria, along with its presumed cognate response regulator MtrA and the lipoprotein LpqB. Here, we postulate a possible role for LpqB in the MtrAB signal transduction pathway. We discuss what is known about this pathway in the actinobacteria and offer insights into why an essential response regulator does not necessarily need its cognate sensor kinase for activation.