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PROTEIN TRAFFICKING AND LOCALIZATION

PROTEIN TRAFFICKING AND LOCALIZATION. PROTEINS SYNTHESIZED IN CYTOPLASM, BUT BECOME LOCALIZED IN CYTOPLASM CYTOPLASMIC MEMBRANE PERIPLASM OUTER MEMBRANE RELEASED IN ENVIRONMENT HOW? WHAT IS MECHANISM(S) OF LOCALIZATION?.

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PROTEIN TRAFFICKING AND LOCALIZATION

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  1. PROTEIN TRAFFICKING AND LOCALIZATION • PROTEINS SYNTHESIZED IN CYTOPLASM, BUT • BECOME LOCALIZED IN • CYTOPLASM • CYTOPLASMIC MEMBRANE • PERIPLASM • OUTER MEMBRANE • RELEASED IN ENVIRONMENT • HOW? WHAT IS MECHANISM(S) OF LOCALIZATION?

  2. INSERTION OF INTEGRAL CYTOPLASMIC MEMBRANE PROTEINS – AN EXAMPLE • CYTOPLASMIC MEMBRANE PROTEINS CONTAIN “SIGNAL SEQUENCE” - 15 - 30 HYDROPHOBIC AMINO ACID RESIDUES NEAR THE N-TERMINUS [e.g., GLYCINE, ALANINE, VALINE, LEUCINE, PHENYLALANINE] SIGNAL SEQUENCE ALLOWS PROTEIN TO BIND MEMBRANE AND BE SOLUBLE IN THE PHOSPHOLIPID MATRIX. • AND TRANS-MEMBRANE-SPANNING SEQUENCES - HYDROPHOBIC • SIGNAL RECOGNITION PARTICLE • SRP BINDS NASCENT PROTEIN (BEING TRANSLATED) AND DELIVERS TO • MEMBRANE BOUND RECEPTOR • RECEPTOR PROTEIN DELIVERS NASCENT MEMBRANE PROTEIN TO TRANSLOCON • TRANSLOCON INSERTS NASCENT MEMBRANE PROTEIN INTO CYTOPLASMIC MEMBRANE WITH MEMBRANE-SPANNING REGIONS • TRAVERSING MEMBRANE

  3. RIBOSOME mRNA 1 PROTEIN SYNTHESIS STARTS ON RIBOSOME [N-TERMINUS SYNTHESIZED FIRST] NASCENT INTEGRAL MEMBRANE PROTEIN MEMBRANE SPANNING 2 SRP BINDS SIGNAL AND TRANSPORTS TO RECEPTOR SIGNAL SEQUENCE 3 RECEPTOR FACILITATES NASCENT PROTEIN BINDING TO TRANSLOCON SRP 4 TRANSLOCON FACILITATES INSERTION INTO CYTOPLASMIC MEMBRANE (SIGNAL & MEMBRANE-SPANNING) CYTOPLASMIC MEMBRANE RECEPTOR PERIPLASM TRANSLOCON

  4. NADH DEHYDROGENASE CYTOPLASM MEMBRANE SPANNING SEQUENCES APPRECIATE!! CM

  5. PROTEIN EXPORT INTO PERIPLASMIC SPACE FOUR NECESSARY COMPONENTS IN MECHANISM • SIGNAL SEQUENCE WHICH IS CLEAVED - [NEAR N-TERMINAL]: • SOME HYDROPHILIC AMINO ACIDS [e.g., ARGININE, GLUTAMATE] • FOLLOWED BY HYDROPHOBIC AMINO ACIDS • FOLLOWED BY ALANINE/X/ALANINE • CYTOPLASMIC CHAPERONE TO PRESENT UN-FOLDED PROTEIN TO TRANSLOCON • TRANSLOCON IN CYTOPLASMIC MEMBRANE TO TRANSLOCATE PROTEIN ACROSS CYTOPLASMIC MEMBRANE [N-TERMINUS FIRST] • SIGNAL PEPTIDASE - ENZYME WHICH CLEAVES OFF THE SIGNAL AFTER ALANINE/X/ALANINE

  6. 3 4 5 1 mRNA 2 RIBOSOME CHAPERONE DELIVERS UNFOLDED PROTEIN TO TRANSLOCON PROTEIN DESTINED FOR PERIPLASM SIGNAL TRANSLOCON SIGNAL PEPTIDASE TRANSLOCON - PUMPS PROTEIN THROUGH CELL MEMBRANE. N-TERMINUS EMBEDDED IN CELL MEMBRANE. CYTOPLASM N CYTOPLASMIC MEMBRANE PERIPLASM SIGNAL SEQUENCE COMPLETELY DEGRADED SIGNAL SEQUENCE CLEAVED AND PROTEIN FOLDS IN PERIPLASM

  7. PILUS ASSEMBLY: CHAPERONE - USHER PATHWAY • P PILI - COMPOSED OF SIX STRUCTUAL PROTEINS • ALL SIX TRANSPORTED ACROSS CYTOPLASMIC MEMBRANE • CHAPERONE CATALYZES PROPER FOLDING IN PERIPLALSM AND DELIVERS SUBUNITS TO USHER IN OUTER MEMBRANE ADHESIN LINKERS PILIN MOLECULES PILUS CHANNEL USHER (PORE) OUTER MEMBRANE PERIPLASMIC CHAPERONE CONDUCTS TO USHER EXPORT ACROSS CYTOPLASMIC MEMBRANE CYTOPLASM

  8. TAKE AWAY: UNDERSTAND – PROTEINS MUST BE LOCALIZED TO PERFORM THEIR FUNCTION. CYTOPLASMIC MEMBRANE LOCALIZATION – STEPS & FACTORS INVOLVED PERIPLASMIC SPACE LOCALIZATION – STEPS & FACTORS INVOLVED PILUS ASSEMBLY HOW ARE THOSE PROTEINS RECOGNIZED/MARKED FOR THOSE DESTINATIONS? WHAT ARE THE SIGNALS? WHAT FACTORS RECOGNIZE & ACT ON THE SIGNALS?

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