Main Ideas - Many proteins can't fold into their final conformation by themselves, need chaperones!- Common chaperones: heat shock proteins Hsp60 and Hsp70, lectin chaperones in ER!- Protein folding occurs via multiple binding and release steps by the chaperones!- The proteasome deliberately destroys aberrant proteins!- The ubiquitin-conjugating systems consists of E1-E2-E3; it can be activated by various mechs and causes poly-ubiquitination of target proteins!- Degrons on proteins turn them into degradation targets!- In the ER, N-linked oligosaccs are used as tags to mark the state of protein folding!- The unfolded protein response activates txn of chaperone genes to help the cell cope w/misfolded proteins!!Learning Objectives 1) Understand the concept of protein chaperones - Protein folding in the cytoplasm and the ER - some proteins translated straight into the cyto and some are translocated into the ER during translation!- some prots begin to fold WHILE being synthesized --> inital folding of protein completed after release from the ribosome!- some freshly syn. prots can form compact domain structures w/most of the final secondary features (molten globule), quickly achieved, dynamic and flexible straight...slow process of real folding to finish !- Chaperone mediated folding - most prots probs don't fold before synthesis is completed!- each domain of a new pros quickly gets to a molten globule state --> subsequent folding is slow, involves multiple steps that req. a chaperone!- protease pathways for proteins that are wrong (have introns, incorrect aa seq, taking too long, etc).!- once protein is grabbed by protease it's over!- Chaperones: Hsp60 and Hsp70 - help prots fold to correct conformation!- high affinity to hydrophobic patches because these parts SHOULD be inside the protein, so something is wrong if Hsp see them (aka why it's good to have a high affinity)!- both utilize ATP to reg. protein folding!- diff. structures: Hsp70 tightly folded, docks on proteins as they come out of the rib. Hsp60 acts later, often part of complexes.! 2) Know the imp elements of the proteasome - Proteasome!- 4 stacks of heptameric rings, proteases face the inside!- disp. thru cyto and nucleus!- regulatory particle= the top, what recognizes the target prot w/polyubi chain 3) Be able to describe the ubiquitin-conjugating system - see below!- E1: ubi activating enzyme!- E2: what conjugates it to target protein!- E3: what gives us specificity, many targets, recognizes the degradation signal and holds the protein!- E2/E3: ubi ligase unit - Induce protein degradation 1) Activate ubi ligase: phosphorylation, ligand binding, or protein subunit addition (last 2= allosteric reg)!2) Activation of degradation signal on protein: phosphorylation, unmasking by protein degradation, or creation of destabilizing N-terminus 4) Understand the elements of the unfolded protein response - Protein folding and degradation in the ER!- have chaperones in the ER, ex. Lectin!- makes sure thru multiple rounds of sugering (glucose) and desugering that the protein gets folding properly and can exit from the ER!- Export of misfolded prots from the ER!- misfolded soluble or membrane proteins are translocated from the ER back to the cytosol and degraded in the proteasome via ER protein translocator!- Unfolded protein response!- the proteins involved are transmembrane proteins --> able to sense misfolded proteins in the ER lumen --> signal to nucleus/genes --> get txn of genes that increase protein folding capacity !- see more below!!!!!!!!!Kinase --> senses misfolded protein --> dimerizes and autophosphorylates --> they turn into an endoribonuclease (there are certain mRNAs that aren't fully spliced, they get exported to the cytoplasm) --> the endorib. will act as spliceosome and cut that mRNA intron --> makes a diff. mRNA --> makes a gene regulatory protein --> enters the nucleus and activates genes encoding ER chaperones --> help fold
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