Protein trafficking and localization
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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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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?


Protein trafficking and localization

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


Protein trafficking and localization

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


Protein trafficking and localization

NADH DEHYDROGENASE

CYTOPLASM

MEMBRANE SPANNING

SEQUENCES

APPRECIATE!!

CM


Protein trafficking and localization

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


Protein trafficking and localization

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


Protein trafficking and localization

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


Protein trafficking and localization

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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