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BSCI443: Microbial Physiology > Lecture 5: Protein Export > Flashcards

Lecture 5: Protein Export Flashcards

1
Q

Localization Signal

A

Portion of the polypeptide usually in the primary sequence that acts as a signal for where the protein needs to go. Often on N-terminus

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2
Q

Secretion Signal

A

One of the localization signals whose cleavage can reduce improper folding which may negatively impact normal cell processes
-Characteristic features include partially conserved sequence of amino acids and location in nascent polypeptides
-Recognized by a specific secretion system
-May not be present in the mature protein

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3
Q

Most proteins in the outer membrane

A

Beta barrels

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4
Q

Most proteins in the inner membrane

A

Alpha helix transmembrane domain

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5
Q

Sec/Tat dependent secretion system

A

-In gram positive: Movement of protein from inner membrane to the outer membrane
-In gram negative: Into the periplasm

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6
Q

Type 2 secretion system

A

Gets protein out of the cell past the outer membrane completely

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7
Q

Type 5 secretion system

A

Gets protein INTO the outer membrane

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8
Q

Common characteristics of all protein secretion systems

A

-All involve multi protein complexes to cross on or more membranes
-Structurally unique from one another
-Each has a unique mailing label in the nascent polypeptide
-Secrete different proteins
-Have some kind of energy source to drive membrane translocation
-Many translocation systems use cytoplasmic chaperones to restrict folding of the peptide until secreted

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9
Q

Sec-dependent secretion systems (3 characteristics)

A

-Dominant protein secretion mechanism that crosses cytoplasmic/inner membrane
-Present in ALL bacteria
-Contains a N-terminal secretion signal

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10
Q

SecYEG/BA characteristics

A

-In both gram positive and negative
-Transport of unfolded proteins

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11
Q

SecYEG/BA Mechanism

A

-SecB recognizes a secretion signal and acts as a chaperone to transport and prevent unfolding towards YEG
-SecA uses ATPase activity (ATP hydrolysis) that guides the unfolded protein through SecYEG via translocation
-Secretion signal is cleaved (Usually from N-term)

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12
Q

SecSRP chracteristics

A

-Both gram positive & gram negative
-Cotranslational Transport
-Uses signal recognition particle (SRP) to for secretion signal recognition
-N-term is synthesized first by ribosome in order for it to be recognized by SecYEG

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13
Q

SecSRP Mechanism

A

-SRP binds to co-translated protein from ribosome while still attached
-FtsY uses GTPase activity to dock the ribosome-SRP complex to SecYEG
-SecYEG supports translocation INTO the membrane to become an intermembrane protein

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14
Q

Twin Arginine Translocation (TAT) secretion system pathway characteristics

A

-Found in gram positive & gram negative bacteria
-Transports (FOLDED) proteins
-Uses proton motive force as energy

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15
Q

TAT secretion system pathway

A

-TatB and TatC bind N-terminal peptide with twin arginines
-TatB and TatC recruit this peptide to TatA that acts as a membrane channel for translocation

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16
Q

Tat secretion system in gram negative bacteria

A

Proteins will either remain within the cytoplasm or be exported by Type II secretion systems

17
Q

Type II Secretion System

A

Sec/TAT-dependent secretion to the periplasm
MOSTLY GRAM NEGATIVE
-Secretion signal I removed
-Secretes folded proteins
-N-term secretion signal II directs the periplasmic polypeptide to the GSP
-GSP system uses cytoplasmic ATP to export protein

18
Q

Three domains of Type V Secretion System Autotransporter Secretion

A

-N-terminal secretion signal (Cleaved in periplasm)
-B-barrel domain (Pore in the outer membrane)
-Passenger domain (Remain attached or cleaved)

19
Q

Two partner secretion system of type 5 secretion system

A

-One partner carries B-barrel domain
-Other partner is secreted
-Transports some large virulence factors (Usually its partner)

20
Q

Steps of autotransporter secretion in Type V secretion systems

A

-Secretion across inner membrane by Sec
-Signal I is removed in periplasm
-B-domain forms pore helped by Bam complex
-Passenger domain passes out of cell through B-domain pore
-Passenger domain forms the active protein

21
Q

Type I secretion system

A

-Translocator composed of 3 proteins
-Single step to cross both membranes (Mainly in gram neg)
-ATP driven, resembles transporters for small molecules
-Secretion signal within C-term

22
Q

3 proteins of the Type I translocator

A

-Cytoplasmic ATPase
-Periplasmic tube
-Outer membrane port

23
Q

Steps of Type I Secretion system

A

-Polypeptide translated by cytoplasmic ribosomes
-Protein not correctly folded
-C-term secretion signal docks with ABC subunit via ATPase activity
-Polypeptide exported across inner membrane, periplasm, and outer membrane in a single step
-ATP hydrolysis
-Secreted protein refolds

24
Q

Examples of proteins who use T1SS

A

-RTS (repeats-in-toxin) toxin
-Cell surface protein
-Proteases
-Lipases
-Bacteriocins
-Heme-acquisition proteins
-Nodulation-related proteins

25
Q

Type III secretion system

A
26
Q

Type III Secretion System Characteristics

A

-Polypeptide synthesis: N-term signal made & binds to multi-cargo chaperone
-Complex docks with cytoplasm face of secretion system
-ATP used to load protein into central lumen (protein remains unfolded)
-Protein released at the tip of the protein like a syringe

27
Q

Similarities between Type III Secretion systems and flagellum

A

Type 3 secretion systems and flagellar assembly machinery look alike, have similar component and functions in a similar manner. Only differ since flagella use proton gradient while T3SS uses ATP hydrolysis

28
Q

Type IV Secretion System Characteristics

A

-Composed of different proteins than other systems
-Secretes proteins and/or DNA
-ATP dependent
-Carried by many pathogenic bacteria (Conjugation, DNA Uptake, Effector translocation)
-Both gram negative and gram positive cells

29
Q

Type IV Secretion System Process

A

One step process
-Proteins synthesized in cytoplasm
-Signal can vary
-Proteins loaded into lumen of a translocated protein
-Pump-like secretion
-May not require pilus but they may still be attached

30
Q

Type VI Secretion System effectors

A

-Peptidoglycan-degrading enzymes
-Membrane targeting enzymes
-Nucleases

31
Q

Type VI Secretion System Process

A

-Effectors assembled into apparatus
-Released upon “Firing”
-Signal unknown
-Recycling of apparatus component

32
Q

Differences in secretion systems in gram positive bacteria

A

-Sec/TAT
-Additional proteins for Sec
-Injectosome similar to T3SS
-Mechanism unclear

33
Q

Type VII Secretion System in mycobacteria

A

-Cross mycomembrane heavily modified by lipids
-Sec/TAT-independent

BSCI443: Microbial Physiology (10 decks)

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