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Chapter 8 : Type IV Secretion Systems

Author: Drusilla L. Burns1
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Affiliations: 1: Food and Drug Administration, 8800 Rockville Pike, Bethesda, MD 20892
Content Type: Monograph
Publication Year: 2003

Category: Bacterial Pathogenesis

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Abstract:

Type IV transporters differ from other transporter systems in that type IV systems are used not only to transport proteins but also to mobilize DNA. In fact, it is likely that type IV transporters first evolved as conjugation systems that functioned to transfer genetic information between bacteria and only later were these systems modified by pathogenic bacteria to transfer critical virulence factors across the bacterial membranes and into the host eukaryotic cell. Since transfer of genetic information from one bacterium to another via bacterial conjugation is an ancient system that likely predates the evolution of pathogens and therefore predates the necessity to transport virulence factors across bacterial membranes, it seems likely that the first type IV transporter was a conjugation system that transferred DNA from one bacterium to another. A slight variation of type IV DNA transport systems appears to have occurred when type IV systems evolved that solely transport proteins without any DNA attached. Pathogens that produce type IV transporters include , spp., , , , and . is the causative agent of the disease pertussis, or whooping cough. This pathogen secretes one of its important virulence factors, pertussis toxin (PT), using a type IV transporter. Several intracellular pathogens utilize type IV transporters to export important virulence factors from the bacterium to the cellular milieu of the host cell.

Citation: Burns D. 2003. Type IV Secretion Systems, p 115-128. In Burns D, Barbieri J, Iglewski B, Rappuoli R (ed), Bacterial Protein Toxins. ASM Press, Washington, DC. doi: 10.1128/9781555817893.ch8

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Type IV Secretion Systems
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Citation: Burns D. 2003. Type IV Secretion Systems, p 115-128. In Burns D, Barbieri J, Iglewski B, Rappuoli R (ed), Bacterial Protein Toxins. ASM Press, Washington, DC. doi: 10.1128/9781555817893.ch8
/content/10.1128/9781555817893.chap8.fig8-1
Figure 1

Schematic diagram of the events that occur during bacterial conjugation. The donor bacterium attaches to the recipient cell by its pilus. The pilus retracts and a mating channel is formed through which the DNA passes. After replication of the DNA is complete, the two bacteria separate, each now carrying its own copy of the plasmid. Adapted from reference 2 with permission.

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10.1128/9781555817893/fig8-1.gif
Image of Figure 1
Figure 1

Schematic diagram of the events that occur during bacterial conjugation. The donor bacterium attaches to the recipient cell by its pilus. The pilus retracts and a mating channel is formed through which the DNA passes. After replication of the DNA is complete, the two bacteria separate, each now carrying its own copy of the plasmid. Adapted from reference 2 with permission.

Citation: Burns D. 2003. Type IV Secretion Systems, p 115-128. In Burns D, Barbieri J, Iglewski B, Rappuoli R (ed), Bacterial Protein Toxins. ASM Press, Washington, DC. doi: 10.1128/9781555817893.ch8
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Figure 2

The family of type IV transporters. Shown are homologies between the genes encoding the VirB transporter of , closely related genes of transfer regions of conjugative plasmids, and the genes of transport systems of pathogenic bacteria. Also shown is the relationship between the genes of the transfer regions of the ColIb-P9 plasmid and the genes of the system.

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Image of Figure 2
Figure 2

The family of type IV transporters. Shown are homologies between the genes encoding the VirB transporter of , closely related genes of transfer regions of conjugative plasmids, and the genes of transport systems of pathogenic bacteria. Also shown is the relationship between the genes of the transfer regions of the ColIb-P9 plasmid and the genes of the system.

Citation: Burns D. 2003. Type IV Secretion Systems, p 115-128. In Burns D, Barbieri J, Iglewski B, Rappuoli R (ed), Bacterial Protein Toxins. ASM Press, Washington, DC. doi: 10.1128/9781555817893.ch8
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Figure 3

Schematic model of the structure of the VirB transporter. Proteins encoded by the genes of form a pilus structure. Most of the VirB proteins are believed to associate to form this structure, which begins in the inner membrane, spans the periplasmic space and the outer membrane, and then extends into the extracellular space.

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10.1128/9781555817893/fig8-3.gif
Image of Figure 3
Figure 3

Schematic model of the structure of the VirB transporter. Proteins encoded by the genes of form a pilus structure. Most of the VirB proteins are believed to associate to form this structure, which begins in the inner membrane, spans the periplasmic space and the outer membrane, and then extends into the extracellular space.

Citation: Burns D. 2003. Type IV Secretion Systems, p 115-128. In Burns D, Barbieri J, Iglewski B, Rappuoli R (ed), Bacterial Protein Toxins. ASM Press, Washington, DC. doi: 10.1128/9781555817893.ch8
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Figure 4

Subunit structure of PT. PT is composed of an enzymatically active S1 subunit and a component, known as the B oligomer, which binds to receptors on eukaryotic cells. The structure of PT is typical of a family of bacterial toxins that have an AB structure, in that it is composed of an enzymatically active subunit and five subunits that form the ring of the binding component.

10.1128/9781555817893/fig8-4_thmb.gif
10.1128/9781555817893/fig8-4.gif
Image of Figure 4
Figure 4

Subunit structure of PT. PT is composed of an enzymatically active S1 subunit and a component, known as the B oligomer, which binds to receptors on eukaryotic cells. The structure of PT is typical of a family of bacterial toxins that have an AB structure, in that it is composed of an enzymatically active subunit and five subunits that form the ring of the binding component.

Citation: Burns D. 2003. Type IV Secretion Systems, p 115-128. In Burns D, Barbieri J, Iglewski B, Rappuoli R (ed), Bacterial Protein Toxins. ASM Press, Washington, DC. doi: 10.1128/9781555817893.ch8
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Figure 5

Mechanisms of transport by type IV systems. Type IV transporters exhibit several mechanisms by which they introduce virulence factors into eukaryotic cells. In the case of , PT is secreted directly into the extracellular mileu. The toxin then binds to the eukaryotic cell and enters the cell via an endocytic pathway. In contrast, the type IV transporters of and are capable of injecting virulence factors directly into the eukaryotic cell. The type IV transporter injects a nucleic acid substrate whereas the type IV transporter injects a protein substrate.

10.1128/9781555817893/fig8-5_thmb.gif
10.1128/9781555817893/fig8-5.gif
Image of Figure 5
Figure 5

Mechanisms of transport by type IV systems. Type IV transporters exhibit several mechanisms by which they introduce virulence factors into eukaryotic cells. In the case of , PT is secreted directly into the extracellular mileu. The toxin then binds to the eukaryotic cell and enters the cell via an endocytic pathway. In contrast, the type IV transporters of and are capable of injecting virulence factors directly into the eukaryotic cell. The type IV transporter injects a nucleic acid substrate whereas the type IV transporter injects a protein substrate.

Citation: Burns D. 2003. Type IV Secretion Systems, p 115-128. In Burns D, Barbieri J, Iglewski B, Rappuoli R (ed), Bacterial Protein Toxins. ASM Press, Washington, DC. doi: 10.1128/9781555817893.ch8
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References

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1. Berger, B. R.,, and P. J. Christie. 1994. Genetic complementation analysis of the Agrobacterium tumefaciens operon: virB2 through virB11 are essential virulence genes. J. Bacteriol. 176: 3646– 3660.
2. Firth, N.,, K. Ippen-Ihler,, and R. A. Skurray,. 1996. Structure and function of the F factor and mechanism of conjugation. In F. C. Neidhardt,, R. Curtiss III,, J. L. Ingraham,, E. C. C. Lin,, R. B. Low,, B. Magasanik,, W. S. Reznikoff,, M. Riley,, M. Schaechter,, and H. E. Umbarger (ed.), Escherichia coli and Salmonella, Cellular and Molecular Biology, 2nd ed. American Society for Microbiology, Washington, D.C.
3. Fullner, K. J.,, J. C. Lara,, and E. W. Nester. 1996. Pilus assembly by Agrobacterium TDNA transfer genes. Science 273: 1107– 1109.
4. Higashi, H.,, R. Tsutsumi,, S. Muto,, T. Sugiyama,, T. Azuma,, M. Asaka,, and M. Hatakeyama. 2002. SHP-2 tyrosine phosphatase as an intracelllular target of Helicobacter pylori CagA protein. Science 295: 683– 686.
5. Lai, E.-M.,, and C. I. Kado. 1998. Processed VirB2 is the major subunit of the promiscuous pilus of Agrobacterium tumefaciens. J. Bacteriol. 180: 2711– 2727.
6. Nagai, H.,, J. C. Kagan,, X. Zhu,, R. A. Kahn,, and C. R. Roy. 2002. A bacterial guanine nucleotide exchange factor activates ARF on Legionella phagosomes. Science 295: 679– 682.
1. Lessel, M.,, D. Balzer,, W. Pansegrau,, and E. Lanka. 1992. Sequence similarities between the RP4 Tra2 and the Ti VirB region strongly support the conjugation model for T-DNA transfer. J. Biol. Chem. 267: 20471– 20480.
2. Vogel, J. P.,, and R. R. Isberg. 1999. Cell biology of Legionella pneumophila. Curr. Opin. Microbiol. 2: 30– 34.

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