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Microbial Physiology notes lec13 10-25-10

Microbial Physiology notes lec13 10-25-10 - Microbial...

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Microbial Physio Lecture 13: Motility and Chemotaxis Involving Bacterial Flagelli continued October 25, 2010 Material not discussed in class, but are responsible for!! Note: Chemotaxis is called positive if movement is in the direction of a higher concentration of the chemical in question, and negative if the direction is opposite. 1. –Attractant ( w/o attractant bound to MCP) causes weaker interactions between intersubunit periplasmic domains and intersubunit cytoplasmic domains as compared w/ +Attractant ( w/ attractant bound to MCP) a. When there is no attractant bound, the MCP subunits are in a loose conformation therefore subunit exchange can occur b. When there is attractant bound, the MCP subunits are in a tight conformation therefore subunit exchange cant occur 2. Almost all amino acid replacements in TMS1 results in counter clockwise rotation of flagella a. i.e there is weaker TM1:TM2 interactions, stronger intersubunit interactions and poor signaling 3. Intrasubunit movement (TM1 relative to TM2) may initiate signaling a. i.e attractant binding causes 1 of the 2 TMs in the membrane to shift relative to the other one there is relative displacement of the 2 TMs in the membrane 4. attractant binding to MCP causes a conformational change so that the MCP is a poor substrate of CheB(de-methylates) and a good substrate for CheR(methylates) a. methylation by S-adenosylmethionine (SAM) the affinity of the MCP for the bound attractant the MCP dimer gets looser w/ increase methylation b. maybe attractant binding frees up Glu (glutamate) residues for increased hydration which results in negative charges the negative charges cause electrostatic repulsion resulting in a conformational changes c. methylation removes the negative charges, and the proteins return to its previous, more folded conformation
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d. want to be able to the affinity of the MCP to the attractant so that the bacteria is able to sense different [ ]’s 1. Both the MCP conformation and the cheB activity determine the MCP methylation state 2. Note: glutamate alanine mutations in an MCP blocks adaptation, but some adaptation still occurs due to cooperativity that results from methylation changes in OTHER MCPs. 3. Receptor complexes: a. Built out of trimers and dimers a 2D hexagonal lattice ( built from trigonal units) b. c. Each cheA dimer is shared by 2 units each unit differs with respect to its composition containing variable #’s of the 5MCPs. i. Minor MCPs show amplification 4. proposed mechanism of MCP action: a. a piston like displacement of 1 TMS in the monomer relative to the other is the primary signal b. subunit interactions plays a role: i. mutant MCPs (Tar) results in CCD form oligomers ii. CW form no oligomers c. Lateral signaling w/in the MCP lattice can occur d. Attractant promotes supramolecular complex formation this gives rise to sigmoidal kinetic responses by the kinase CheA e. Repellent
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Microbial Physiology notes lec13 10-25-10 - Microbial...

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