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?
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
RIBOSOME
mRNA
1 PROTEIN SYNTHESIS STARTS ON RIBOSOME
[N-TERMINUS SYNTHESIZED FIRST]
NASCENT INTEGRAL
MEMBRANE PROTEIN
2 SRP BINDS SIGNAL AND
TRANSPORTS TO RECEPTOR
MEMBRANE
SPANNING
SIGNAL
SEQUENCE
3 RECEPTOR FACILITATES NASCENT
PROTEIN BINDING TO TRANSLOCON
4 TRANSLOCON FACILITATES
INSERTION INTO CYTOPLASMIC
MEMBRANE (SIGNAL &
MEMBRANE-SPANNING)
SRP
CYTOPLASMIC
MEMBRANE
PERIPLASM
RECEPTOR
TRANSLOCON
NADH DEHYDROGENASE
CYTOPLASM
APPRECIATE!!
CM
MEMBRANE SPANNING
SEQUENCES
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
1
mRNA
2
RIBOSOME
SIGNAL
PROTEIN
DESTINED FOR
PERIPLASM
TRANSLOCON
CYTOPLASM
CYTOPLASMIC
MEMBRANE
CHAPERONE
DELIVERS UNFOLDED
PROTEIN TO
TRANSLOCON
SIGNAL PEPTIDASE
N
PERIPLASM
4
SIGNAL SEQUENCE CLEAVED AND
PROTEIN FOLDS IN PERIPLASM
3
TRANSLOCON - PUMPS
PROTEIN THROUGH CELL
MEMBRANE. N-TERMINUS
EMBEDDED IN CELL
MEMBRANE.
5 SIGNAL
SEQUENCE
COMPLETELY
DEGRADED
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
PILUS
ADHESIN
LINKERS
PILIN
MOLECULES
CHANNEL
USHER (PORE)
PERIPLASMIC CHAPERONE CONDUCTS TO USHER
EXPORT ACROSS CYTOPLASMIC MEMBRANE
CYTOPLASM
OUTER MEMBRANE
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?