Bacterial Secretion Systems Flashcards
(48 cards)
What are the 4 functions of secretion systems?
Protection = secrete toxins
Transport of structural proteins
Communication
Adhesion (fimbriae/pili)
What are the two mechanisms of secretion in Gram-negative bacteria?
One-step process = across the cell membrane and outer membrane in one step
Two-step process = export into the periplasm (Sec/Tat system) and then export across the outer membrane
What are the secretion systems used in one-step and two-step processes in Gram-negative bacteria?
One-step = T3SS, T4SS, T6SS
Two-step = T2SS, T5SS
What is the mechanism of secretion in Gram-positive bacteria?
Secreted proteins are commonly translocated across the CM by the Sec pathway or Tat pathway
What does the Sec system do?
Translocates unfolded proteins
Recognizes a hydrophobic leader sequence and is present in the cytoplasm of all bacteria
What does the Tat system do?
Transport folded proteins
Present in many bacteria and associate with proteins with cofactors
What is the energy source for both the Sec and Tat systems?
ATP
What does T1SS do?
They are dedicated to transporting one or a few unfolded substrates that range in function
Substrates are generally sec-independent and typically contain a C-terminal signal sequence that is recognized by T1SS and remains uncleaved
What are the 3 major components of the T1SS?
ABC transporter
MFP = membrane fusion protein
OMP = outer membrane protein transporter
What does the MFP of T1SS do?
Connects and coordinates transport across the CM and the OM
What provides the energy from T1SS?
ATP hydrolysis
What do OMFs provide?
A trans-periplasmic channel penetrating the outer membrane and connects to the MFP
What connects the OMF and the ABC in the periplasmic space of T1SS?
MFP
What does T1SS secrete from UPEC and what does it do?
Alpha-hemolysin which allows further invasion of the urinary tract
What is the T1SS toxin, MARTX, secreted from and what does it do?
V. cholera
Facilitates colonization of the small intestine by destroying host actin cytoskeleton
What Gram stain is T2SS found in?
Gram negative
What is the T2SS also known as and why?
The Sec-dependent system
Many proteins that pass through the T2SS must first reach the periplasm via the Sec pathway
Which pathogens require T2SS for virulence?
V, cholera, L, pneumonphila, enterotoxigenic E. coli
What are some virulence determinants secreted via the T2SS?
The ADP-ribosylating toxins of E. coli
Cholera toxin
Exotoxin A of P. aeruginosa
How does T2SS work?
In the CM, there is a platform that anchors T2SS
Unfolded proteins enter the periplasm via Sec and folds in the periplasm
The outer membrane complex is a complex of secretion that transports the folded proteins
Which bacteria are type III secretion systems found in?
Gram-negative bacteria - both pathogenic and non-pathogenic
What is the machinery in type III secretion systems?
The injectisome
Delivers effector proteins across bacterial and host membranes into the cytosol of host cells
What host cell functions do T3SS secretion systems modulate and how many membranes does it cross?
Immune and defense responses
3 membranes, CM + OM + target PM
What is the structure of injectisomes?
Composed of a series of basal rings that span the bacterial inner and outer membranes and are connected to a hollow needle (in Yersina) or filament (in Salmonella)
Each structure is tipped with a translocation pore that is inserted into the plasma membrane of the target cell
