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Identification of the minimal cytolytic unit for streptolysin S and an expansion of the toxin family

BACKGROUND: Streptolysin S (SLS) is a cytolytic virulence factor produced by the human pathogen Streptococcus pyogenes and other Streptococcus species. Related “SLS-like” toxins have been characterized in select strains of Clostridium and Listeria, with homologous clusters bioinformatically identifi...

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Autores principales: Molloy, Evelyn M., Casjens, Sherwood R., Cox, Courtney L., Maxson, Tucker, Ethridge, Nicole A., Margos, Gabriele, Fingerle, Volker, Mitchell, Douglas A.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: BioMed Central 2015
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4513790/
https://www.ncbi.nlm.nih.gov/pubmed/26204951
http://dx.doi.org/10.1186/s12866-015-0464-y
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author Molloy, Evelyn M.
Casjens, Sherwood R.
Cox, Courtney L.
Maxson, Tucker
Ethridge, Nicole A.
Margos, Gabriele
Fingerle, Volker
Mitchell, Douglas A.
author_facet Molloy, Evelyn M.
Casjens, Sherwood R.
Cox, Courtney L.
Maxson, Tucker
Ethridge, Nicole A.
Margos, Gabriele
Fingerle, Volker
Mitchell, Douglas A.
author_sort Molloy, Evelyn M.
collection PubMed
description BACKGROUND: Streptolysin S (SLS) is a cytolytic virulence factor produced by the human pathogen Streptococcus pyogenes and other Streptococcus species. Related “SLS-like” toxins have been characterized in select strains of Clostridium and Listeria, with homologous clusters bioinformatically identified in a variety of other species. SLS is a member of the thiazole/oxazole-modified microcin (TOMM) family of natural products. The structure of SLS has yet to be deciphered and many questions remain regarding its structure-activity relationships. RESULTS: In this work, we assessed the hemolytic activity of a series of C-terminally truncated SLS peptides expressed in SLS-deficient S. pyogenes. Our data indicate that while the N-terminal poly-heterocyclizable (NPH) region of SLS substantially contributes to its bioactivity, the variable C-terminal region of the toxin is largely dispensable. Through genome mining we identified additional SLS-like clusters in diverse Firmicutes, Spirochaetes and Actinobacteria. Among the Spirochaete clusters, naturally truncated SLS-like precursors were found in the genomes of three Lyme disease-causing Borrelia burgdorferi sensu lato (Bbsl) strains. Although unable to restore hemolysis in SLS-deficient S. pyogenes, a Bbsl SLS-like precursor peptide was converted to a cytolysin using purified SLS biosynthetic enzymes. A PCR-based screen demonstrated that SLS-like clusters are substantially more prevalent in Bbsl than inferred from publicly available genome sequences. CONCLUSIONS: The mutagenesis data described herein indicate that the minimal cytolytic unit of SLS encompasses the NPH region of the core peptide. Interestingly, this region is found in all characterized TOMM cytolysins, as well as the novel putative TOMM cytolysins we discovered. We propose that this conserved region represents the defining feature of the SLS-like TOMM family. We demonstrate the cytolytic potential of a Bbsl SLS-like precursor peptide, which has a core region of similar length to the SLS minimal cytolytic unit, when modified with purified SLS biosynthetic enzymes. As such, we speculate that some Borrelia have the potential to produce a TOMM cytolysin, although the biological significance of this finding remains to be determined. In addition to providing new insight into the structure-activity relationships of SLS, this study greatly expands the cytolysin group of TOMMs. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12866-015-0464-y) contains supplementary material, which is available to authorized users.
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spelling pubmed-45137902015-07-25 Identification of the minimal cytolytic unit for streptolysin S and an expansion of the toxin family Molloy, Evelyn M. Casjens, Sherwood R. Cox, Courtney L. Maxson, Tucker Ethridge, Nicole A. Margos, Gabriele Fingerle, Volker Mitchell, Douglas A. BMC Microbiol Research Article BACKGROUND: Streptolysin S (SLS) is a cytolytic virulence factor produced by the human pathogen Streptococcus pyogenes and other Streptococcus species. Related “SLS-like” toxins have been characterized in select strains of Clostridium and Listeria, with homologous clusters bioinformatically identified in a variety of other species. SLS is a member of the thiazole/oxazole-modified microcin (TOMM) family of natural products. The structure of SLS has yet to be deciphered and many questions remain regarding its structure-activity relationships. RESULTS: In this work, we assessed the hemolytic activity of a series of C-terminally truncated SLS peptides expressed in SLS-deficient S. pyogenes. Our data indicate that while the N-terminal poly-heterocyclizable (NPH) region of SLS substantially contributes to its bioactivity, the variable C-terminal region of the toxin is largely dispensable. Through genome mining we identified additional SLS-like clusters in diverse Firmicutes, Spirochaetes and Actinobacteria. Among the Spirochaete clusters, naturally truncated SLS-like precursors were found in the genomes of three Lyme disease-causing Borrelia burgdorferi sensu lato (Bbsl) strains. Although unable to restore hemolysis in SLS-deficient S. pyogenes, a Bbsl SLS-like precursor peptide was converted to a cytolysin using purified SLS biosynthetic enzymes. A PCR-based screen demonstrated that SLS-like clusters are substantially more prevalent in Bbsl than inferred from publicly available genome sequences. CONCLUSIONS: The mutagenesis data described herein indicate that the minimal cytolytic unit of SLS encompasses the NPH region of the core peptide. Interestingly, this region is found in all characterized TOMM cytolysins, as well as the novel putative TOMM cytolysins we discovered. We propose that this conserved region represents the defining feature of the SLS-like TOMM family. We demonstrate the cytolytic potential of a Bbsl SLS-like precursor peptide, which has a core region of similar length to the SLS minimal cytolytic unit, when modified with purified SLS biosynthetic enzymes. As such, we speculate that some Borrelia have the potential to produce a TOMM cytolysin, although the biological significance of this finding remains to be determined. In addition to providing new insight into the structure-activity relationships of SLS, this study greatly expands the cytolysin group of TOMMs. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12866-015-0464-y) contains supplementary material, which is available to authorized users. BioMed Central 2015-07-24 /pmc/articles/PMC4513790/ /pubmed/26204951 http://dx.doi.org/10.1186/s12866-015-0464-y Text en © Molloy et al. 2015 This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
spellingShingle Research Article
Molloy, Evelyn M.
Casjens, Sherwood R.
Cox, Courtney L.
Maxson, Tucker
Ethridge, Nicole A.
Margos, Gabriele
Fingerle, Volker
Mitchell, Douglas A.
Identification of the minimal cytolytic unit for streptolysin S and an expansion of the toxin family
title Identification of the minimal cytolytic unit for streptolysin S and an expansion of the toxin family
title_full Identification of the minimal cytolytic unit for streptolysin S and an expansion of the toxin family
title_fullStr Identification of the minimal cytolytic unit for streptolysin S and an expansion of the toxin family
title_full_unstemmed Identification of the minimal cytolytic unit for streptolysin S and an expansion of the toxin family
title_short Identification of the minimal cytolytic unit for streptolysin S and an expansion of the toxin family
title_sort identification of the minimal cytolytic unit for streptolysin s and an expansion of the toxin family
topic Research Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4513790/
https://www.ncbi.nlm.nih.gov/pubmed/26204951
http://dx.doi.org/10.1186/s12866-015-0464-y
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