Functional Study Of Histidine Kinase VicK In Streptococcus Mutans

Microorganism use two-component systems as signal-transduction systems which involves two conserved components,a histidine kinase and a response regulator.The histidine kinase is activated by environmental stimuli,autophosphorylates at a conserved histidine residue.The phosphorylated histidine kinase will create a high-energy phosphoryl group.This phosphoryl group is subsequently transferred to an aspartate residue in the conjugated response regulator.Phosphorylation induces a conformational change in the receiver domain.The conformational change will activate the effector domain which effects the response.These simple signal transduction systems could ensure microorganism to sense the complicated changes in the environment and take appropriate response.In this thesis,we studied two-component systems in Streptococcus mutans.VicK is a histidine kinase and VicR is conjugated response regulator.According to the sequence conservation of VicK,we generated three mutations D441A,W443A and A439 in VicK.We found these mutations had changed phosphothasnferase and phosphatase activity,but had not changed kinase activity.By homologous recombination,we generated three mutated strains and compared there ability to form biofilm.In A439,the transcription and expression level of GtfD was up-regulated while GtfB,GtfC and GbpC were down-regulated.Cultured these four strains in glucose-containing media,UA159 and D441A could form a thick,smooth and EPS(extracellualr polysaccharide)riched biofilms whereas W443A and ?439 could only form a thin,rough and breakable biofilms which contained a little EPS compared to UA159.In conclusion,VicK plays a major role in regulating EPS.