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MCB 121 Lecture 16

MCB 121 Lecture 16 - MCB 121 Lecture 16 I Regulated...

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MCB 121 - Lecture 16 I. Regulated proteolysis II. Biotech Applications - Protein production A) Enzymes B) Drugs ----------------------------------------------------------------------------------------------------------------------------- Regulation of Transcription Regulation of Processing (through regulated splicing) Regulation of Transcript stability (smRNA pathway and degradation of RNA) Regulation of translation Regulation of Protein stability (ubiquitin/proteasome pathway) ------------------------------------------ * enzyme that cut protein does not require ATP; it is an energy yielding reaction. * it is presumed that degradation of protein inside the cell doesn't require energy and follow the same type of pathway Degradation Protein amino acid However, in vitro system, proteins are not degraded anymore in the cell extract when ATP is removed. => intracellular protein degradation requires ATP => almost all proteins degraded by the system called (Ubiquitin/proteasome system) * ubiquitin = tag that marks protein for degradation * proteasome = protein that act as degradation machine. Ubiquitin: - First identified in 1977 as a histone modification in mammals = found histone has 76aa-protein attached to it = this protein is attached by "isopeptide linkage" - Ubiquitin linked at C- terminus to ε-lysyl groups on proteins via isopeptide bond O Ub - C N - (CH2)4 - C - H . N - H * C-terminus of ubiquitin is hooked on ε-lysyl group of lysine of the target protein
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* Lysine 48 of the ubiquitin has another Ub hooked on. - 76 aa, 8.5 kDa small protein found in all eukaryotes, highly conserved sequence - ubiquitin is higher conserved between species Ubiquitination can target proteins for degradation - ubiquitin ligases can add chains of ubiquitin to target proteins (UbK48 connects links in chain) - general system targets improperly folded proteins (all proteins that are not folded properly) - specific ubiquitin ligases (E3 proteins) target specific proteins for regulated degradation. Two roles: 1. get rid of the miss-folded proteins that can cause problem in the cell 2. specifically get rid of the protein at certain time because development of some physiological process requires the lost of those proteins. The ubiquitination Pathway: Step 1- ubiquitin monomer is present and ATP is used to activate E1 enzyme => So Ub is attached to cysteinyl group of E1 enzyme by a thioester linkage => E1 = ubiquitin activating (UBA) enzyme - catalyzes the activation of ubiquitin that is required for attachment to targets - activation via ubiquitin adenylylation (hence ATP requirement here)
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MCB 121 Lecture 16 - MCB 121 Lecture 16 I Regulated...

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