Microbial Physiology notes lec12 10-20-10

Microbial Physiology notes lec12 10-20-10 - Microbial...

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Microbial Physiology Lecture 12: Motility and Chemotaxis Involving Bacterial Flagelli October 20, 2010 E. coli: o Lateral flagella are propellers they rotate because they have a sinusoidal wave form in the flagella, when rotating, it give rise to forward motion, just as a propeller on the back of a ship o The lateral flagella forms a bundle being the bacterium and when they are showing the tuft(bundle), they are moving forward and that is because rotation is in the counter clockwise (CCW) direction o When rotation of lateral flagella is in the clockwise (CW) direction then they are tumbling the lateral flagella don’t form a bundle in the back of the bacterium, instead the flagella are dispersed, and that is because all of the flagella are now tangled up and are functioning independently of each other instead of coordinately Negative cooperativity of the MCP’s allows responses over a 10 5 fold range from about <1 µM >10mM and this is due to the polar clumping of receptors and receptor methylation o The 5 MCPs in E.coli: Tsr, Tar, Trg, Tap, Aer Tsr= transducer towards serine Tar=transducer towards aspartate Trg= transducer towards ribose and galactose Tap= transducer towards amino acids and peptides Aer: aerotxis These are all of the MCP’s in E.coli, there are no other MCP’s, but there are other bacteria that have as many as 100 MCPs The ratios of MCPs there is much more Tsr(11x’s as much) and Tar(6x’s as much) than there is Trg, Tap, and Aer The MCPs still participate in the formation of the lattice The MCP’s all form a polar lattice( a clump/cluster) of proteins all of the 5 MCPs are randomly inserted into the cluster Signaling: The MCPs binds to the attractant/ repellent this then causes the MCP’s to give rise to a response and cause a conformational change in the MCP’s truly in response to the changing [ ] gradients of the attractants/ repellents o MCPs can also bind to the proteins that bind the attractants/repellents As a result of changing conformation of MCP it causes a conformational change in che W which is the
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transducer which transduces the signal from MCP to che A Repellent bound MCPs stimulates the autokinase activity of CheA Attractant bound MCPs inhibit the autokinase activity of cheA This is a crucial fact for when the activation of the signal (when the MCPs senses the attractant/repellent), and for the adaptation ( methylation of MCP—which occurs much more slowly) o Che A autophosphorylates when the MCP is bound to a repellent o Che A-phosphate is in equilibrium with Che-Y- phosphate(response regulator) when you increase the amount of phosphorylation of A, you increase the same amount of phosphorylation of Y o Che-Y in its un-phosphorylated form has high affinity for che A, but once che-Y is phosphorylated it no longer has affinity for che A instead che-Y interacts with the basal region of the flagellum
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Microbial Physiology notes lec12 10-20-10 - Microbial...

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