BIO 3153 Lecture Notes - Lecture 12: Signal Peptidase, Alpha Helix, Transmembrane Protein
15 Dec 2017
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Lecture 12 protein sorting ii: protein sorting to er. Ribosomes associate with mrna, make polypeptide chain fold and catalyze synthesis of protein, either free or membrane bound, requires signal sequence to be directed to er. Signal sequence once in translocator it guides polypeptide chain through to. 1) recognition binding of srp to signal peptide causes pause in translation. 2) targeting complex binds to srp receptor, signal resumes translation, signal sequence initiates translocation. 3) release signal sequence binds to translocator and is slowly brought through, translocation of protein into er lumen or integration of transmembrane protein. 4) recycling complex dissociates and is reused. Overview start-transfer signal, cleaved by peptidase to fold/release, release of polypeptide to lumen and signal sequence to membrane. Double pass: internal signal sequence initiates translocation, stop transfer signal stops translocation, both are alpha helices and released to membrane, negative end goes in first, no cleaving of signal sequences.
