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Microbial Physiology notes lec21 11-15-10

Microbial Physiology notes lec21 11-15-10 - Microbial...

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Microbial Physio Lecture 21: Chaperones continued November 15, 2010 Proteosome and chaperone relationship: a. Chaperones try to refold proteins until it becomes its native form, and if it cant, then the chaperone passes the unfolded, or partially unfolded protein onto a proteasome degrades the protein b. The proteasomes are essentially the same from bacteria eukaryotes, in all cases they consist of rings that form a chamber which are called nanochambers either for folding or degradation purposes i. Nanochambers consists of 7 subunits which can be all of the same type or of a different type subunit 1. i.e they can be homologous but encoded by different genes, or they can all be exactly the same subunit that is encoded by a single gene 2. there are 7 of the subunits in a circle that makes a chamber 3. in the case of the proteasomes there are 2 separate subunits, the alpha and the beta subunits, 2 rings of each type of subunit, that makes up the chamber 4. then there is a lid, which is the case of the proteasomes can be inhibitory, in the case of the chaperones can be activating(stimulatory) c. there are all types of variation on the theme, but there is a striking similarity between the chaperones and proteasomes in the fact that there is 7 membered rings which is rather unusual in biology for both the chaperones and proteasomes, so based on those observations, it was then proposed that the compartments—nano chambers arose just once and then was shared by the chaperones and proteasomes The question now is exactly what the mechanism is: a. Part of the mechanism involves exposure to both hydrophobic and hydrophilic surfaces simultaneously, because a folded protein, lets say it’s a water soluble protein, then normally that protein has a hydrophobic core and its surface is covered by hydrophilic residues which interact favorably w/ the aqueous environment, and the hydrophobic core is never exposed to that aqueous environment once its folded b. This is quite a task you have to overcome the free energy of folding, but also have to be able to fold and refold and unfold and refold because sometimes the protein folding goes down the wrong pathway, which is a dead end and it could lead to a partially folded protein, but its not the protein that is needed for the final product, which is generally one of the lowest free energy i. a protein that has gone down the wrong pathway of folding to a dead end, cant be unfolded, is a protein that is destined to be degraded by the proteasome
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ii. this seems to be a large waste, but in fact it isn’t because the cell in general can reutilize all of the building blocks once the proteins are degraded, and the same is believed to be true for the degradation of nucleic acids—both RNA and DNA, although it seems to not be as efficient in these cases because it turns out bacteria export out the cell a large amount of nucleotides, so they aren’t reusing the nucleotides when they have an excess of them Steps for folding of proteins w/in nano compartment of chaperonin system:
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Microbial Physiology notes lec21 11-15-10 - Microbial...

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