Microbial Physiology notes lec14 10-27-10

Microbial Physiology notes lec14 10-27-10 - Microbial...

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Microbial Physio Lecture 14: Sensing Physical Forces by E.coli October 27, 2010 Thermosensing in E.coli 1. All 4 MCPs are thermosensors a. This year it was also discovered that aer, one of the 5 total MCP also is a thermosensor 2. a. Tar the aspartate receptor i. Can be warm and cold sensor ii. Of course there is an optimum temperature for the bacteria 1. the purpose of human body temp getting warmer is to fight off disease most bacteria that are pathogens have an optimal temp. at exactly human optimal temperature 3. a. If it’s a warm sensor when temp bacteria smooth swim, and when the bacteria goes to lower temperature the response will be to tumble i. used when want to get to warmer temperatures b. If it’s a cold sensor when temp bacteria smooth swim, and when bacteria go to higher temperature the response will be tumbling i. used when want to get to cooler temperatures c. Of course there is an optimum temperature for the bacteria i. Tar can be a warm and a cold sensor but it cant be both at the same time because that would cause total confusion of Tar, and bacteria wouldn’t get anywhere 4. Tar has 4 methylation sites: a. There are 4 glutamates near the binding site for CheR—which is the methyltranferase which methylates the glutamate; and cheB which demethylates the 4 glutamates b. c. If you look at the DNA/amino acid sequence you see that 2 of the amino acids are glutamines and 2 are glutamates 1. glutamines are very stable, its just an amide that doesn’t hydrolyze
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2. glutamine in 2 positions on the MCP and glutamate in 2 positions on the MCP gives a neutral sensor that doesn’t sense temperature at all 3. But the enzyme that takes the amides off the glutamine to convert it to glutamate which can be methylated, while the glutamine residues cant be methylated the enzyme that does this is cheB a. cheB is a methylesterase! So how can cheB also get rid of the amide groups on the glutamine?? i. Because the residues on which cheB can act are exactly the same residues that can be methylated and demethylated ii. Therefore cheB has 2 enzymatic fxns: 1. deamination of the 4 glutamines acts as a hydrolase for amides on the glutamine a. only as long as cheB is present, if not, then the MCP becomes an inadequate sensor w/ respect to adaptation particularly b. once get deamination from glutamine glutamate it is permenant and remains this way and therefore remains functional indefinitely 2. demethylation of glutamates b. Che R is the methyltransferase that transfers the methyl groups onto the glutamate, but cant to glutamine
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Microbial Physiology notes lec14 10-27-10 - Microbial...

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