Structural And Functional Investigation Of Vibrio Alginolyticus FadR

FadR is a type of global regulator with a diverse set of members exclusively distributed in y-proteobacteria.Unlike E.coli FadR,the paradigm member,Vibrio FadR orthologues exhibit the strikingly-superior ability to sense the available fatty acids in ecological niches.However,the molecular mechanism underlying this unusual scenario is not well understood.Here we reported this case.Crystal structure of V.alginolyticus FadR revealed an extra helix-rich domain mainly formed by the 40-redisue insert.Unexpectedly,subsequent complex structural analyses of V.alginolyticus FadR bound to palmitoyl-CoA revealed that distinct from the E.coli FadR with only one ligand site,Vibrio FadR had one more ligand-binding site constituted mainly by this 40-redisue insert.Furthermore,the ligand binding to V.alginolyticus FadR leads to more seriously conformational alteration in N-terminal DNA-binding domain than that of E.coli FadR,which fits well to its super-sensing to long chain fatty acids.Three types of different Vibrio FadR proteins were prepared.Surface plasmon resonance(SPR)validated the binding of Vibrio FadR orthologues to cognate DNA targets.Isothermal titration calorimetry(iTC)-based analyses showed that binding of Vibrio FadR to the palmitoyl-CoA ligand was distinct from that its E.coli counterpart.Apparently,Vibrio FadR having two ligand-binding sites represents a new mechanism for fatty acid sensing.Given the role of FadR in virulence of certain species of Vibrionaceae,it is rational that development of small molecule drugs/inhibitors targeting the FadR-mediated fatty acid sensing might be a promising therapeutics against Vibrio infections.