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Insights into pneumococcal fratricide from the crystal structures of the modular killing factor LytC

Abstract

The first structure of a pneumococcal autolysin, that of the LytC lysozyme, has been solved in ternary complex with choline and a pneumococcal peptidoglycan (PG) fragment. The active site of the hydrolase module is not fully exposed but is oriented toward the choline-binding module, which accounts for its unique in vivo features in PG hydrolysis, its activation and its regulatory mechanisms. Because of the unusual hook-shaped conformation of the multimodular protein, it is only able to hydrolyze non–cross-linked PG chains, an assertion validated by additional experiments. These results explain the activation of LytC by choline-binding protein D (CbpD) in fratricide, a competence-programmed mechanism of predation of noncompetent sister cells. The results provide the first structural insights to our knowledge into the critical and central function that LytC plays in pneumococcal virulence and explain a long-standing puzzle of how murein hydrolases can be controlled to avoid self-lysis during bacterial growth and division.

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Figure 1: 3D structure of LytC–choline–PG ternary complex.
Figure 2: Localization of GFP-LytC, properties of Q1 chimeric protein, and differential behavior between LytC and Cpl-1.
Figure 3: Proposed interaction between LytC and PG substrate attached to teichoic acid chains.
Figure 4: Superimposition of LytC–choline–PG and Cpl-1–(2S5P)2 crystallographic complexes onto larger PG framework as deduced by its NMR structure22.

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Acknowledgements

We are indebted to E. García for his critical reading of the manuscript, to B. de las Rivas (Instituto de Fermentaciones Industriales, Consejo Superior de Investigaciones Científicas) for the generous gift of the GFP-LytC clone and to M.T. Seisdedos for skillful guidance with the fluorescence study. This work was supported by grants from the Spanish Ministry of Science and Technology (BFU2008-01711, SAF2006-00390), EU-CP223111 (CAREPNEUMO, European Union), the COMBACT program (S-BIO-0260/2006) and CIBER de Enfermedades Respiratorias (CIBERES). CIBERES is an initiative of Instituto de Salud Carlos III. The work in the US was supported by the US National Institutes of Health. W.V. was supported by the European Commission (EUR-INTAFAR project). I.P.-D. was a fellow of the Consejo Superior de Investigaciones Científicas.

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Contributions

I.P.-D. performed crystallization and structural determination; A.G. and M.M. performed biochemical experiments; R.S. performed crystallization; W.S. and W.V. purified the PG; S.M. synthetized the PG ligands and wrote the manuscript; M.M.-R. wrote the manuscript; J.L.G., P.G. and J.A.H. conceived the study and wrote the manuscript.

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Correspondence to Juan A Hermoso.

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Supplementary Figures 1–6, Supplementary Tables 1 and 2 and Supplementary Methods (PDF 8157 kb)

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Pérez-Dorado, I., González, A., Morales, M. et al. Insights into pneumococcal fratricide from the crystal structures of the modular killing factor LytC. Nat Struct Mol Biol 17, 576–581 (2010). https://doi.org/10.1038/nsmb.1817

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