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Protein Transport - Coggle Diagram
Protein Transport
2 Major Methods of Protein Sorting
cytosolic pathway - proteins localized to the nucleus, peroxisome, and mitochondria/chloroplast translated by cytosolic ribosomes
Secretory Pathway- includes all secreted proteins, Er, Golgi, Lysosome, and membrane proteins
A. proteins initially translated on Cytosolic ribosomes
B. specific AA sequence on N-term binds to Signal recognition (SRP, a complex of small RNA and 6 proteins) which pauses translation
C. SRP/ribosome/polypeptide binds to receptor on RER surface
D. SRP dissociates as ribosome/polypeptide is translocated to channel in RER membrane called trans Locon
E. polypeptide is transported into RER through channel as translation continues, signal peptide is cleaved off during transport co-translational transport instead of post-translational)
F. protein folds into its active conformation once inside RER lumen
Transport to Plasma Membrane
secretory protein moves through golgi and is released from trans golgi in transport vesicle continuous secretion) or secretory vesicle regulated secretion)
. vesicle fuses with plasma membrane and contents are released (secretory vesicles only fuse with membrane in response to hormone/nerve signal)
Transport to lysosome M6P pathway) – sorting occurs in trans golgi
in cis golgi carbohydrate Mannose on lysosomal protein is Phosphorylated only lysosomal proteins)
phosphate on lysosomal protein binds to receptor in trans golgi
receptor moves to pit region in trans golgi coated with fibrous protein calledclatherin then a vesicle is formed
clatherin-coated vesicle loses clatherin and fuses with endosome (low pH)
phosphate comes off lysosomal protein and protein is released from receptor
transport vesicle forms from endosome and fuses with lysosome
proteins that are localized to the nucleus contain a specific AA sequence called Nuclear localization signals (NLS)
protein binds alpha subunit of importin via NLS
beta subunit of Importin binds
Importin/protein complex passes through NPC via interaction between beta importin and nucleoporins of NPC
interaction of Importin complex with Ran/GTP causes release of protein
Mitochondria and Chloroplasts
translation of protein completed on cytosolic ribosome
chaperone Hsc70 binds to the N-term. of protein and uses ATP to keep protein in unfolded state (DOES NOT BIND TO signal sequence
Hsc70 delivers protein to receptor on outer membrane of mitochondrion (protein binds receptor via matrix targeting sequence
protein transferred to channel protein import pore where outer membrane contacts inner membrane) via signal sequence
protein is transported through import pore into matrix (transport requires ATP hydrolysis by Hsc70)
Hsc70 released, signal sequence is removed by a protease, and protein folds into active conformation