The dissertation is focused on the role of chemotaxis receptor played in the transmembrane signaling. The first project accomplished was to study the interaction between serine receptor and methyltransferase. As an effort to probe the regulation mechanism of methyltransferase CheR, Isothermal Titration Calorimetry (ITC) was applied to characterize any possible regulation associated allosteric effect between methyltransferase CheR\u27s multiple interactions. It was found that methyltransferase CheR binds to its receptor docking site and substrate SAH independently, further experiments are proposed to explore the interaction between the receptor methylation region and methyltransferase, CheR. It is speculated that conformational change in the receptor upon ligand binding controls the accessibility of the receptor methylation region to methyltransferase. The second project was carried out as a continued effort to determine the receptor ligand binding activity in the ternary complex with the adaptor protein CheW and the histidine kinase CheA, and it was expected that some cooperativity between receptor dimers would be observed. Surprisingly, in the absence of the cytoplasmic signaling proteins, CheW and CheA, serine receptors exhibited negative cooperativity in ligand binding between dimers, and the negative cooperavtivity disappeared in detergent solution. For the first time, direct evidence was found as a strong support the transmembrane signaling mechanism that involves receptor clusters. Chemoreceptors form patches at the poles of bacteria in the presence and absence of signaling proteins, and the active interaction between receptor dimers could play a significant role in information integration when passing through the bacterial membrane. Experiments are also designed for further clarify the function of receptor cluster in the future
