Microbial Physiology notes lec13 10-25-10

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

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
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
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
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
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 01/09/2011 for the course BIMM 130 taught by Professor Saier during the Fall '10 term at UCSD.

Page1 / 8

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

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online