The Structural And Functional Studies Of Potassium-sensing Two-component System Related Complexes From Escherichia Coli

Two-component systems(TCS),one of most important signal transduction systems in microorganisms,enable bacteria to sense and transfer environmental signals to induce appropriate cellular responses.TCS can directly or indirectly respond to hundreds of signals,like temperature,nutrients,antibiotics and pH.A typical TCS consists of a sensor histidine kinase embedded on cell membrane(HK)and a cognate cytoplasmic response regulator(RR),which normally functions as an transcriptional regulator.Upon sensing the environmental stimuli,HK undergoes autophosphorylation that conserved histidine residue is phosphorylated.Subsequencely,the phosphoryl group on the histidine is transferred to a conserved aspartate residue in the RR.Such a phosphoryltranser process prompts RR to bind with specific promoters of genes with increased binding affinity to regulate transcription and expression.Given the critical importance of TCS in bacteria,a detailed understanding of the underlying mechanisms involving in signal transduction might contribute to development of next-generation antibiotics.Great advances have been made in understanding signal perception of HK,gene regulation for RR and HK/RR specific interaction during last decades.Currently,a prevailing model for the interaction of HK and RR is that the receiver domain(RD)of RR is mainly responsible for specific interaction with its cognate HK,In this thesis,however,we reported a complete novel interaction model that RR applies both RD and DNA-binding domain(DBD)to interact with its HK.A complex structure of KdpD with KdpE,one of most important TCSs for potassium homeostasis in E.coli,reveals extensive interactions with both RD and DBD involved.In addition,a structure of KdpD complex with PtsN,an accessory KdpD activator,unveiled the details for KdpD/PtsN interaction and proposed the potential model for the accelerated kinase activity of KdpD by PtsN.In summary,this thesis demonstrated a conceivable novel molecular mechanism for the process of KdpD/KdpE signal transduction and regulation,which provided a new direction for investigating the signal transduction of TCS.