The Crystal Structures Of Histidine Kinase YycG In Active And Inactive State

Two-component signal transduction system(TCS),consisting of a histidine kinase and its cognate response regulator,is an important and efficient signaling pathway in bacteria.YycFG TCS is highly conserved and specific to several low G+C Gram-positive bacteria,among which there are a number of important pathogens,including Staphylococcus aureus,Streptococcus pneumoniae and Enterococcus faecium.YycFG TCS is essential for cell wall metabolism,biofilm formation and antibiotic resistance.But the mechanism of YycFG medicated signal transduction remains abscure.Here,we report two different crystal structures of YycG(370-610)protein in active state and in inactive state.The active state structure of YycG is bound with ADP in the active pocket.One CA domain moves to the conserved histidine on the DHp domain,while al helix of the DHp domain that contains the histidine is bending toward the CA domain to lead to a close contact of histidine and ADP.Another CA domain in the active state structure remains further away from histidine even though there is also ADP ligand in active site.Therefore,the active YycG adopts an asymmetric structure in presence of ATP.In contrast,YycG changes to an inactive conformation in absence of ATP.The inactive state structure is rather symmetric.Both CA domains are far away from DHp domain,which is exactly the same as inactive chain of the active state.Accordingly,all DHp helixes are straight.The binding of nucleotides with YycG quanitified by isothermal titration calorimetry experiment indicated ATP and ADP bind the CA domain at a similar affinity although both are at low affinity of 200-400 uM range.In addition,molecular dynamic simulation of the DHp domain supported an alternate bending model as we proposed recently.Together,our studies revealed active and inactive states of YycG structures that can be switched by ATP/ADP binding,in coordination with alternating DHp bends.