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Architecture of the type IV coupling protein complex of Legionella pneumophila

Abstract

Many bacteria, including Legionella pneumophila, rely on the type IV secretion system to translocate a repertoire of effector proteins into the hosts for their survival and growth. Type IV coupling protein (T4CP) is a hexameric ATPase that links translocating substrates to the transenvelope secretion conduit. Yet, how a large number of effector proteins are selectively recruited and processed by T4CPs remains enigmatic. DotL, the T4CP of L. pneumophila, contains an ATPase domain and a C-terminal extension whose function is unknown. Unlike T4CPs involved in plasmid DNA translocation, DotL appeared to function by forming a multiprotein complex with four other proteins. Here, we show that the C-terminal extension of DotL interacts with DotN, IcmS, IcmW and an additionally identified subunit LvgA, and that this pentameric assembly binds Legionella effector proteins. We determined the crystal structure of this assembly and built an architecture of the T4CP holocomplex by combining a homology model of the ATPase domain of DotL. The holocomplex is a hexamer of a bipartite structure composed of a membrane-proximal ATPase domain and a membrane-distal substrate-recognition assembly. The presented information demonstrates the architecture and functional dissection of the multiprotein T4CP complexes and provides important insights into their substrate recruitment and processing.

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Figure 1: Crystal structures of DotL(656–783)–IcmSW and DotL(590–659)–DotN.
Figure 2: Crystal structure of DotL(656–783)–IcmSW–LvgA.
Figure 3: Structural reconstitution of DotL(590–783)–DotN–IcmSW–LvgA.
Figure 4: Effector protein binding.
Figure 5: Model for the T4CP holocomplex.
Figure 6: C-terminal extension of T4CPs.

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Acknowledgements

This study made use of Beamlines 4C and 5C at Pohang Accelerator Laboratory, Korea, and was supported by the National Research Foundation of Korea (NRF) (grant no. 2008-00576) and KAIST Future Systems Healthcare Project, Ministry of Science, ICT and Future Planning. J.D.K. was supported by a TJ PARK postdoctoral fellowship from POSCO TJ PARK Foundation. The authors thank the Korea Institute for Advanced Study for providing computing resources (KIAS Center for Advanced Computation Linux Cluster).

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M.-J.K., J.D.K., H.K., S.K. and Y.-G.K. performed X-ray crystallography and biochemical experiments. C.K. conducted the ALEX-FRET experiment, J.W.B. the SiMPull, K.J. and J.L. homology modelling, and K.S.J. the SAXS. B.-H.O., M.-J.K., J.D.K., N.K.L. and J.U.J. conceived the experiments and wrote the manuscript. All authors discussed the results.

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Correspondence to Byung-Ha Oh.

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The authors declare no competing financial interests.

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Kwak, MJ., Kim, J., Kim, H. et al. Architecture of the type IV coupling protein complex of Legionella pneumophila. Nat Microbiol 2, 17114 (2017). https://doi.org/10.1038/nmicrobiol.2017.114

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