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Protein targeting(vani ma'am)291020
Proteins must be targeted to the correct organelle to perform their functions. There are two main pathways for protein targeting: co-translational and post-translational. In co-translational targeting, proteins destined for the endoplasmic reticulum have signal sequences that target them during synthesis via the signal recognition particle and translocon complex. In post-translational targeting, proteins are synthesized and targeted after synthesis via targeting sequences and receptor proteins to their destinations like the nucleus, mitochondria, and peroxisomes. Chaperones assist in protein folding and translocation complexes facilitate transport across membranes.
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Protein targeting(vani ma'am)291020
- 1. PROTEIN TARGETING G AARATHILFA II M.Sc.ADVANCED BIOCHEMISTRY
- 2. This Photo byUnknown Author is licensed under CC BY
- 3. PROTEIN TARGETING • Proteinsmust be correctly Localized to perform proper function • Receptors for plasma protein • DNA polymerase in nucleus • Catalase in peroxisome • And insulin outside • All proteins begin to be synthesized on cytosolic ribosomes .
- 4. • Sorting ortranslocation can occur @ co – translational @ post – translational This Photo by Unknown Author is licensed under CC BY
- 5. PROTEIN Cytosolic function Synthesis(free ribosomes) peptides released (into cytosol) PROTEIN Nucleus / Mitochondria / Peroxisome synthesis (cytosolic ribosomes) peptides released (cytosol; to be sorted later/ post translationally) PROTEIN cell/ membrane nascent peptide targeted to ER (becomes rough) sorting (co translationally)
- 6. # POST TRANSLATIONALTARGETING . Cytoplasm . Nucleus . Mitochondria . Peroxisome # CO TRANSLATIONAL TARGETING (SECRETORY PATHWAY) . ER . Golgi . Lysosomes . Plasma Membrane
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- 8. SIGNAL PEPTIDE • shortpeptide (16 – 30 amino acid long) • can be cleaved later by signal peptidase or remain as a permanent part of protein • Can be located on N-, C- terminus or in the middle of the protein Mostly N- terminus for secretory pathway.
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- 12. # Most mitochondrialproteins are encoded by nuclear DNA # Only few are encoded by mitochondrial DNA and synthesized on mitochondrial ribosomes This Photo by Unknown Author is licensed under CC BY-SA-NC
- 13. Mitochondrial targeting signal Usuallylocated at N- terminus of precursor polypeptide Generally removed in mitochondrial matrix
- 14. RECEPTOR/ TRANSLOCATION CHANNELIN Mt • TOM – translocase of the outer mitochondrial membrane • TIM – translocase of inner memberane
- 15. • mitochondrial proteinare synthesised in cytosol as precursors • bind to cytosolic chaperone (HSP 70) to keep them unfolded until they are ready to be translocated • energy from ATP
- 18. COMPARISION OF MtAND CHLOROPLAST
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- 20. PEROXISOMES • Single membraneorganelle • Matrix contains oxidative enzymes lipid oxidation without ATP production • Proteins encoded by nuclear DNA (everything is imported)
- 21. TRANSPORT INTO PEROXISOME •Proteins are synthesized and fully folded in cytosol • Completely functional and completely folded protein is transported • This import requires ATP hydrolysis
- 22. PEROXISOME TARGETING SEQUENCES: PTS1 on C-terminus (Ser-Lys-Leu) PTS2 on N-terminus (fewer proteins)
- 23. PEROXISOME TRANSPORT RECEPTOR Peroxins • Binds to proteins with PTS1 and docks to the translocation channel • Complex transported via membrane • Protein is released • Peroxin is recycled
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- 26. TRANSPORT INTO NUCLEUS •All proteins in nucleus are synthesised in cytoplasm • Examples: histones Ribosomal protein DNA and RNA polymerase Transcription factor
- 27. • Nuclear localizationsequence (NLS) is required for transport • Transport occurs through nuclear pores: Nuclear import receptor(Importin α and β) Energy from GTP GTPase Ran • fully folded proteins are transported
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- 31. CO-TRANSLATIONAL TRANSLOCATION • ERsignal sequence (nascent secretory protein) located at the N- terminus and contains a sequence of hydrophobic amino acids • Binding to ER is achieved by signal recognition particle(SRP) • SRP and SRP receptor delivers the nascent/ribosomal polypeptide complex into translocon (SEC61 complex) • With GTP binding, SRP is dissociated and translocon further carries the translation
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- 35. INSERTION OF MEMBRANEPr INTO ER
- 36. • Membrane andsoluble secretory proteins synthesized on the rough ER undergo four principal modifications before they reach their final destinations: (1) covalent addition and processing of carbohydrates (glycosylation) in the ER and Golgi complex, (2) formation of disulfide bonds in the ER, (3) proper folding of polypeptide chains and assembly of multisubunit proteins in the ER, and (4) specific proteolytic cleavages in the ER, Golgi complex, and secretory vesicles.
- 37. # ADDITION ANDINITIAL PROCESSING
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- 40. # UNFOLDED PROTEINRESPONSE
- 41. #MODIFICATION TO MONITERPr FOLDING and QUALITY CONTROL
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