The Bacterial Intimins and Invasins: A Large and Novel Family of Secreted Proteins

PLOS ONE, Dec 2010

Background Gram-negative bacteria have developed a limited repertoire of solutions for secreting proteins from the cytoplasmic compartment to the exterior of the cell. Amongst the spectrum of secreted proteins are the intimins and invasins (the Int/Inv family; TC# 1.B.54) which are characterized by an N-terminal β-barrel domain and a C-terminal surface localized passenger domain. Despite the important role played by members of this family in diseases mediated by several species of the Enterobacteriaceae, there has been little appreciation for the distribution and diversity of these proteins amongst Gram-negative bacteria. Furthermore, there is little understanding of the molecular events governing secretion of these proteins to the extracellular milieu. Principal Findings In silico approaches were used to analyze the domain organization and diversity of members of this secretion family. Proteins belonging to this family are predominantly associated with organisms from the γ-proteobacteria. Whilst proteins from the Chlamydia, γ-, β- and ε-proteobacteria possess β-barrel domains and passenger domains of various sizes, Int/Inv proteins from the α-proteobacteria, cyanobacteria and chlorobi possess only the predicted β-barrel domains. Phylogenetic analyses revealed that with few exceptions these proteins cluster according to organismal type, indicating that divergence occurred contemporaneously with speciation, and that horizontal transfer was limited. Clustering patterns of the β-barrel domains correlate well with those of the full-length proteins although the passenger domains do so with much less consistency. The modular subdomain design of the passenger domains suggests that subdomain duplication and deletion have occurred with high frequency over evolutionary time. However, all repeated subdomains are found in tandem, suggesting that subdomain shuffling occurred rarely if at all. Topological predictions for the β-barrel domains are presented. Conclusion Based on our in silico analyses we present a model for the biogenesis of these proteins. This study is the first of its kind to describe this unusual family of bacterial adhesins.

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The Bacterial Intimins and Invasins: A Large and Novel Family of Secreted Proteins

et al. (2010) The Bacterial Intimins and Invasins: A Large and Novel Family of Secreted Proteins. PLoS ONE 5(12): e14403. doi:10.1371/journal.pone.0014403 The Bacterial Intimins and Invasins: A Large and Novel Family of Secreted Proteins Saier Jr. 0 Jennifer C. Tsai 0 Ming-Ren Yen 0 Rostislav Castillo 0 Denisse L. Leyton 0 Ian R. Henderson 0 Milton H. 0 Hendrik W. van Veen, University of Cambridge, United Kingdom 0 1 Department of Molecular Biology, University of California at San Diego, La Jolla, California, United States of America, 2 The School of Immunity and Infection, University of Birmingham , Edgbaston, Birmingham , United Kingdom Background: Gram-negative bacteria have developed a limited repertoire of solutions for secreting proteins from the cytoplasmic compartment to the exterior of the cell. Amongst the spectrum of secreted proteins are the intimins and invasins (the Int/Inv family; TC# 1.B.54) which are characterized by an N-terminal b-barrel domain and a C-terminal surface localized passenger domain. Despite the important role played by members of this family in diseases mediated by several species of the Enterobacteriaceae, there has been little appreciation for the distribution and diversity of these proteins amongst Gram-negative bacteria. Furthermore, there is little understanding of the molecular events governing secretion of these proteins to the extracellular milieu. Principal Findings: In silico approaches were used to analyze the domain organization and diversity of members of this secretion family. Proteins belonging to this family are predominantly associated with organisms from the c-proteobacteria. Whilst proteins from the Chlamydia, c-, b- and e-proteobacteria possess b-barrel domains and passenger domains of various sizes, Int/Inv proteins from the a-proteobacteria, cyanobacteria and chlorobi possess only the predicted b-barrel domains. Phylogenetic analyses revealed that with few exceptions these proteins cluster according to organismal type, indicating that divergence occurred contemporaneously with speciation, and that horizontal transfer was limited. Clustering patterns of the b-barrel domains correlate well with those of the full-length proteins although the passenger domains do so with much less consistency. The modular subdomain design of the passenger domains suggests that subdomain duplication and deletion have occurred with high frequency over evolutionary time. However, all repeated subdomains are found in tandem, suggesting that subdomain shuffling occurred rarely if at all. Topological predictions for the b-barrel domains are presented. Conclusion: Based on our in silico analyses we present a model for the biogenesis of these proteins. This study is the first of its kind to describe this unusual family of bacterial adhesins. - Funding: This work was supported by NIH (GM077402) of the National Institutes of Health. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Pathogenic Gram-negative bacteria have developed many distinct secretion mechanisms for the efficient surface display of binding domains that specifically interact with their complementary receptors on host cell surfaces [1,2]. The Intimin/Invasin (Int/ Inv) family of adhesins (TC# 1.B.54) consists of outer membrane (OM) proteins that mediate bacterial attachment to and/or invasion of their host cells [3,4,5,6,7]. The archetypal members of the Int/Inv family are from strains of pathogenic Escherichia coli (Int) and Yersinia spp. (Inv). Intimins, first described by Jerse et al in enteropathogenic and E. coli strains, promote intimate bacterial attachment associated with attaching-effacing lesion formation in the gut mucosa [8,9]. This intimate adherence to host cells is mediated by interaction of Intimin with Tir, a protein secreted directly from the bacterial cytoplasm into the host cell membrane via a type III protein secretion system, and which results in host cell actin reorganization. [6,10,11,12,13,14,15,16,17,18]. In contrast, Invasin, which was first described by Isberg and coworkers, enhances the ability of Yersinia spp. to enter target cells, not by binding to a Tir-like protein, but by binding with high-affinity to multiple members of the b1-chain integrin family of mammalian cell receptors. The function of Invasin has been reiewed elsewhere. The Intimin and Invasin systems have been studied primarily with respect to their contribution to the virulence of Gramnegative pathogens. In contradistinction, little is known of the secretory mechanism of either Intimin or Invasin. These homologous proteins are related to each other both in terms of sequence and predicted structure, possessing a conserved modular organization [2,3,19,20] consisting of (i) an N-terminal signal sequence, (ii) a highly conserved N-terminal b-domain and (iii) a C- (...truncated)


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Jennifer C. Tsai, Ming-Ren Yen, Rostislav Castillo, Denisse L. Leyton, Ian R. Henderson, Milton H. Saier. The Bacterial Intimins and Invasins: A Large and Novel Family of Secreted Proteins, PLOS ONE, 2010, Volume 5, Issue 12, DOI: 10.1371/journal.pone.0014403