Serine Chemotaxis
The of Serine Chemotaxis or can be divided into 4 domains: , , and domain. The cytoplasmic doain includes both a methylation region and a protein interaction region, The methylation region contains 4 glutamic acid residues that are methylated as part of adaptation to an ongoing stimulus, The protein interaction region binds to the histidine kinase CheA and the coupling protein CheW. ligand binding inactivates the kinase. Additionally, there are methylation sites in the cytoplasmic domain.
This structure also shows the
Once the binds to the periplasmic domain,
However, it is not known waht changes in the cytoplasmic domain propagate teh signal 200 Å further to control the activity of the kinase CheA bound at the membrne-distal tip of the recepor. Changes in dynamics of different regions of the receptor have been proposed to propagate he signal. The piston is proposed to stabilize the HAMP domain, destablize teh methylation region, and stabilize the protein interaction region. it causes changes in the dynamics of the chemoreceptor. In the kinase-off state, the HAMP domain becomes, the methylation sites become and the cytoplasmic domain becomes less flexible.
To test the effects of changes to residues in the HAMP domain in the Tsr Receptor, certain residues were mutated. So codon-by-codon mutagenesis was performed on the regions in AS1 and in AS2. 13 of the mutant amino acids were considered either critical or important. Important residues are those residues at which a majority of amino acid replacements demonstrably impaired Tsr function. Critical residues are the ones at which majority of the deleterious replacements produced a complete loss-of-function (null) phenotype. By these criteria, AS1 has one important (P221) and six critical (L218, M222, L225, I229, I232, A233) residues; AS2 has six critical residues (E248, M249, L252, L256, M259, L263).
Function
Motile bacteria like Escherichia coli cells are attracted to and repelled by signals in their surroundings due to transmembrane chemoreceptor proteins, i.e: their direction of movement is controlled by this mechanism. The stimulus information travels through the receptor molecule, shifting the dynamic properties of adjoining structural elements. The section of the found in the cytoplasmic membrane is a helical-bundle structure signaling molecule.
Disease and Relevance
If we can understand[1] how the bacteria moves[1] we might be able to make antibiotics that can target those specific control sites and prevent diseases by halting their search for attractant molecules.
The chemoreceptors Escherichia coli and Salmonella typhimurium[2] are stable and ultrasensitive molecules with coupling proteins, CheW and CheA attached at the bottom. A ligand bound can stimulate change through the kinase control model as a response. Among the 3 kinase control regulations, CheA and CheW binding is done through stable spatial clustering-leading to the YinYang Hypothesis[3]. It proposes that strong helix packing stabilizes the receptor.
Overview of Structure and Mechanism
The section of the found in the cytoplasmic membrane is a helical-bundle structure signaling molecule.
