Structural Research of Type IV Secretion Systems

Inquiry

The type IV secretion system (T4SS) is found in Gram-negative and Gram-positive bacteria and is a functionally diverse translocation superfamily. It typically translocates DNA and effector proteins into eukaryotic target cells by relying on direct cell-to-cell contact. In the past, X-ray crystallography and cryo-electron microscopy have achieved essential milestones in research, gradually revealing the shared structural features of T4SS and how structural variations confer specific functional diversity.

Advances in T4SS research

T4SS consists of two major subfamilies, splicing systems and effector transposons. Splice systems mediate DNA transfer between bacteria and are responsible for rapidly transmitting antibiotic-resistance genes and virulence determinants. Many Gram-negative bacterial pathogens use effector transposons to deliver virulence macromolecules into prokaryotic or eukaryotic cells to regulate physiological processes during infection. Recently, researchers have made great progress in defining the structure of T4SS units and components.

T4SS structural analysis

Researchers demonstrated the cryo-electron microscopy (cryo-EM) structure of the T4SS complex from the R388 plasmid at 2.8 Å resolution. T4SS is found to contain four sub-complexes consisting of 12 proteins (VirB1-VirB11 and VirD4), the outer membrane core complex (OMCC), the stem, the arch, and the inner membrane complex (IMC). In the IMC, six dimers of VirB4 are clustered together, where the interface between two adjacent VirB4 central subunits is distributed over the N- and C-terminal structural domains. The stem is a central conical assembly consisting of VirB6 pentamers and VirB5 pentamers. The arch consists of a hexamer of the homotrimeric unit of VirB8 peri, forming a ring around the stem. The OMCC consists of an O-layer embedded in the outer membrane and an I-layer located below the periplasm.

Figure 1. Composite electron density map (left) and overall model (right) of R388 T4SS. (Macé K, et al., 2022)

Protein	Organism	Method	Resolution	PDB Entry ID
T4SS protein CagL	Helicobacter pylori 26695	X-ray diffraction	3.25 Å	3ZCJ
Dot T4SS OMC	Legionella pneumophila	Cryo-EM single particle analysis	3.5 Å	6X62
Dot T4SS PR	Legionella pneumophila	Cryo-EM single particle analysis	3.7 Å	6X64
Dot/Icm T4SS	Legionella pneumophila	Cryo-EM single particle analysis	3.7 Å	6X65
dDot T4SS OMC	Legionella pneumophila	Cryo-EM single particle analysis	4.2 Å	6X66
CagL-K74	Helicobacter pylori	X-ray diffraction	2.791 Å	4YVM
Stalk complex structure (TrwJ/VirB5-TrwI/VirB6)	Escherichia coli	Cryo-EM single particle analysis	3.7 Å	7O3V
VirB8 domain of PrgL	Enterococcus faecalis	X-ray diffraction	1.735 Å	7AED
Dot/Icm T4SS PR	Legionella pneumophila	Cryo-EM single particle analysis	2.8 Å	7MUE
Dot/Icm T4SS C1	Legionella pneumophila	Cryo-EM single particle analysis	3.8 Å	7MUC
T4SS Protein CagL	Helicobacter pylori 26695	X-ray diffraction	2.15 Å	4CII
The BID Domain of Bep6	Bartonella rochalimae ATCC BAA-1498	X-ray diffraction	2.1 Å	4YK1
CagV, a VirB8 homolog of T4SS	Helicobacter pylori 26695	X-ray diffraction	1.922 Å	6IQT
T4SS protein CagL	Helicobacter pylori 26695	X-ray diffraction	2.201 Å	3ZCI
CagL	Helicobacter pylori 26695	X-ray diffraction	2.3 Å	4X5U
CagX from T4SS	Helicobacter pylori	Cryo-EM single particle analysis	3.8 Å	6OGE
CagT from T4SS	Helicobacter pylori	Cryo-EM single particle analysis	3.8 Å	6OEE
CagY from T4SS	Helicobacter pylori	Cryo-EM single particle analysis	3.8 Å	6ODI
PolyAla model of OMCC I-layer	Helicobacter pylori	Cryo-EM single particle analysis	3.8 Å	6OEH
PolyAla model of the PRC from the type 4 secretion system	Helicobacter pylori	Cryo-EM single particle analysis	3.5 Å	6ODJ
PolyAla model of the O-layer from the type 4 secretion system	Helicobacter pylori	Cryo-EM single particle analysis	3.8 Å	6OEF
TraC	Escherichia coli	X-ray diffraction	3 Å	1R8I
VirB9 C-terminal domain in complex with VirB7 N-terminal domain from T4SS	Xanthomonas citri pv. citri str. 306	SOLUTION NMR	/	2N01
Cagbeta with CagZ	Helicobacter pylori 26695	X-ray diffraction	2.1 Å	6JHO
C13 reconstruction of outer membrane core complex (OMCC) of type IV secretion system (T4SS)	Salmonella enterica subsp. enterica serovar Typhi	Cryo-EM single particle analysis	3.31 Å	7SPB
C17 reconstruction of outer membrane core complex (OMCC) of type IV secretion system (T4SS)	Salmonella enterica subsp. enterica serovar Typhi	Cryo-EM single particle analysis	2.95 Å	7SPC

Table 1. Structural research of the type IV secretion systems.

Creative Biostructure is a leading biological company offering a range of protein structure analysis services including X-ray crystallography, cryo-electron microscopy (cryo-EM), and NMR spectroscopy. Our team of experienced structural biologists has extensive expertise in characterizing membrane protein structures and can provide high-quality structural information for challenging targets.

In addition, we provide related services including protein expression and purification, biophysical characterization, and computational modeling to facilitate new advances in researchers' studies of the structure and action mechanisms of the T4SS. If you are interested in the structural analysis of T4SS or other biomolecules, please feel free to contact us. We are committed to providing high-quality data and support to our clients and look forward to working with you on your structural biology projects.

References

Macé K, et al. Cryo-EM structure of a type IV secretion system. Nature. 2022. 607(7917): 191-196.
Liu X, et al. Structure of a type IV secretion system core complex encoded by multi-drug resistance F plasmids. Nat Commun. 2022. 13(1): 379.
Sheedlo MJ, et al. Molecular architecture of bacterial type IV secretion systems. PLoS Pathog. 2022. 18(8): e1010720.
Christie PJ, et al. Mechanism and structure of the bacterial type IV secretion systems. Biochim Biophys Acta. 2014. 1843(8): 1578-1591.