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Lecture 30

MBIO 4600 Lecture 30: Lecture 30

5 Pages
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Department
Microbiology
Course Code
MBIO 4600
Professor
Brassinga Ann

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Lecture 30
Protein secretion systems
All systems rely on channels in the outer membrane formed from
beta-sheets organized in a ring
Type I
oSecrete a protein directly from the cytoplasm to the outside of
the cell
oATP-binding cassette (ABC) transporter  pushes protein
through channel
Type II
oMulti-protein complex pseudopilus structure
oPushes protein through inner membrane and through secretin
channel to outside of the cell
oClosely related to the transport systems that assemble type IV
pili (i.e. natural competence)
Type III
oSyringe-like structure that injects e'ector proteins through
both bacterial membranes and eukaryotic cells
Type IV (T4SS)
oAncestrally related to conjugation systems
Type IVA IncF (F plasmid)
IncP (RP4 plasmid)
F-T4SS F plasmid 
tra/trb
genes
P-T4SS (
A. tumefaciens
T-DNA) 
vir
genes
I-T4SS (
L. pneumophila
) 
icm/dot
genes
oMulti-subunit cell-envelope-spanning structures compromising
a secretion channel and a pilus
oTransfer both proteins and nucleoprotein complexes
Mediate horizontal gene transfer
Delivery of bacterial e'ector proteins into eukaryotic
host cells
o
A. tumefaciens
Causes Crown Gall disease in plants
T4SS encoded by
vir
operon (11 genes) and
virD4
vir
operon genes essential for DNA transfer
Mediates transfer of oncogenic genes into plant cells
Tumour  disease
Model of T4SS gene functions
VirB2 pilus
VirD4 coupling protein
VirD2 relaxase
VirE3 pulls along ssDNA
o
L. pneumophila
Intracellular parasite of protozoa (natural host)
Infects alveolar macrophages in humans
Remodulates host cell cytoplasm
Delays host cell apoptosis
Core structure conserved
Genomic islands
Bacterium  core genome and 6exible gene pool
oIS, transposons, plasmids, integrons, prophages, and large
unstable regions (islands)
Features of islands
oRegions (10-100 kb) containing clusters of genes that allow
bacterium to occupy speci9c environmental niches
oIncrease bacterial 9tness
oSmaller regions (1-10 kb)  islets
oGC content and codon usage di'ers from rest of chromosome
oUnstable
Carry mobility genes (similar to
int
or transposases)

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Description
Lecture 30 Protein secretion systems All systems rely on channels in the outer membrane formed from betasheets organized in a ring Type I o Secrete a protein directly from the cytoplasm to the outside of the cell o ATPbinding cassette (ABC) transporter pushes protein through channel Type II o Multiprotein complex pseudopilus structure o Pushes protein through inner membrane and through secretin channel to outside of the cell o Closely related to the transport systems that assemble type IV pili (i.e. natural competence) Type III o Syringelike structure that injects effector proteins through both bacterial membranes and eukaryotic cells Type IV (T4SS) o Ancestrally related to conjugation systems Type IVA IncF (F plasmid) IncP (RP4 plasmid) FT4SS F plasmid tratrb genes PT4SS (A. tumefaciens TDNA) vir genes IT4SS (L. pneumophila) icmdot genes o Multisubunit cellenvelopespanning structures compromising a secretion channel and a pilus o Transfer both proteins and nucleoprotein complexes Mediate horizontal gene transfer Delivery of bacterial effector proteins into eukaryotic host cells o A. tumefaciens
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