Transcript Document
Protein degradation rate varies 100x Most have motifs marking them for polyubiquitination: taken to proteosome & destroyed Other signals for selective degradation include PEST & KFERQ • PEST : found in many rapidly degraded proteins • Deletion increases t1/2 10x, adding PEST drops t1/2 10x • Sometimes targets poly-Ub • Recent yeast study doesn’t support general role • KFERQ: cytosolic proteins with KFERQ are selectively taken up by lysosomes in chaperone-mediated autophagy under conditions of nutritional or oxidative stress. Protein degradation in bacteria Also highly regulated, involves chaperone-like proteins 1. Lon (also in mito) Protein degradation in bacteria Also highly regulated, involves chaperone like proteins 1. Lon 2. Clp (also in chloroplasts) Protein degradation in bacteria Also highly regulated, involves chaperone like proteins 1. Lon 2. Clp 3. FtsH in IM (also in cp and mito) PROTEIN TARGETING All proteins are made with an “address” which determines their final cellular location Addresses are motifs within proteins PROTEIN TARGETING All proteins are made with “addresses” which determine their location Addresses are motifs within proteins Remain in cytoplasm unless contain information sending it elsewhere PROTEIN TARGETING Targeting sequences are both necessary & sufficient to send reporter proteins to new compartments. PROTEIN TARGETING 2 Pathways in E.coli http://www.membranetransport.org/ 1. Tat: for periplasmic redox proteins & thylakoid lumen! 2 Pathways in E.coli 1. Tat: for periplasmic redox proteins & thylakoid lumen! • Preprotein has signal seq S/TRRXFLK 2 Pathways in E.coli 1. Tat: for periplasmic redox proteins & thylakoid lumen! • Preprotein has signal seq S/TRRXFLK • Make preprotein, folds & binds cofactor in cytosol 2 Pathways in E.coli 1. Tat: for periplasmic redox proteins & thylakoid lumen! • Preprotein has signal seq S/TRRXFLK • Make preprotein, folds & binds cofactor in cytosol • Binds Tat in IM & is sent to periplasm 2 Pathways in E.coli 1. Tat: for periplasmic redox proteins & thylakoid lumen! • Preprotein has signal seq S/TRRXFLK • Make preprotein, folds & binds cofactor in cytosol • Binds Tat in IM & is sent to periplasm • Signal seq is removed in periplasm 2 Pathways in E.coli http://www.membranetransport.org/ 1. Tat: for periplasmic redox proteins & thylakoid lumen! 2. Sec pathway • SecB binds preprotein as it emerges from rib • Sec pathway SecB binds preprotein as it emerges from rib & prevents folding • • Sec pathway SecB binds preprotein as it emerges from rib & prevents folding Guides it to SecA, which drives it through SecYEG into periplasm using ATP • • • Sec pathway SecB binds preprotein as it emerges from rib & prevents folding Guides it to SecA, which drives it through SecYEG into periplasm using ATP In periplasm signal peptide is removed and protein folds • • • Sec pathway part deux SRP binds preprotein as it emerges from rib & stops translation Guides rib to FtsY FtsY & SecA guide it to SecYEG , where it resumes translation & inserts protein into membrane as it is made Periplasmic proteins with the correct signals (exposed after cleaving signal peptide) are exported by XcpQ system PROTEIN TARGETING Protein synthesis always begins on free ribosomes in cytoplasm 2 Protein Targeting pathways Protein synthesis always begins on free ribosomes in cytoplasm 1) proteins of plastids, mitochondria, peroxisomes and nuclei are imported post-translationally 2 Protein Targeting pathways Protein synthesis always begins on free ribosomes In cytoplasm 1) proteins of plastids, mitochondria, peroxisomes and nuclei are imported post-translationally made in cytoplasm, then imported when complete 2 Protein Targeting pathways Protein synthesis always begins on free ribosomes In cytoplasm 1) Post -translational: proteins of plastids, mitochondria, peroxisomes and nuclei 2) Endomembrane system proteins are imported co-translationally 2 Protein Targeting pathways 1) Post -translational 2) Co-translational: Endomembrane system proteins are imported co-translationally inserted in RER as they are made 2 pathways for Protein Targeting 1) Post -translational 2) Co-translational: Endomembrane system proteins are imported co-translationally inserted in RER as they are made transported to final destination in vesicles SIGNAL HYPOTHESIS Protein synthesis always begins on free ribosomes in cytoplasm in vivo always see mix of free and attached ribosomes SIGNAL HYPOTHESIS Protein synthesis begins on free ribosomes in cytoplasm endomembrane proteins have "signal sequence"that directs them to RER Signal sequence SIGNAL HYPOTHESIS Protein synthesis begins on free ribosomes in cytoplasm endomembrane proteins have "signal sequence"that directs them to RER “attached” ribosomes are tethered to RER by the signal sequence SIGNAL HYPOTHESIS • Protein synthesis begins on free ribosomes in cytoplasm • Endomembrane proteins have "signal sequence"that directs them to RER • SRP (Signal Recognition Peptide) binds signal sequence when it pops out of ribosome & swaps GDP for GTP SIGNAL HYPOTHESIS SRP (Signal Recognition Peptide) binds signal sequence when it pops out of ribosome & swaps GDP for GTP •1 RNA & 7 proteins SIGNAL HYPOTHESIS SRP binds signal sequence when it pops out of ribosome SRP stops protein synthesis until it binds “docking protein”(SRP receptor) in RER SIGNAL HYPOTHESIS SRP stops protein synthesis until it binds “docking protein”(SRP receptor) in RER Ribosome binds Translocon & secretes protein through it as it is made SIGNAL HYPOTHESIS SRP stops protein synthesis until it binds “docking protein”(SRP receptor) in RER Ribosome binds Translocon & secretes protein through it as it is made BiP (a chaperone) helps the protein fold in the lumen SIGNAL HYPOTHESIS Ribosome binds Translocon & secretes protein through it as it is made secretion must be cotranslational