title: Identification of a novel streptococcal adhesin P (SadP) protein recognizing galactosyl-α1-4-galactose-containing glycoconjugates: convergent evolution of bacterial pathogens to binding of the same host receptor.
abstract: Bacterial adhesion is often a prerequisite for infection, and host cell surface carbohydrates play a major role as adhesion receptors. Streptococci are a leading cause of infectious diseases. However, only few carbohydrate-specific streptococcal adhesins are known. Streptococcus suis is an important pig pathogen and a zoonotic agent causing meningitis in pigs and humans. In this study, we have identified an adhesin that mediates the binding of S. suis to galactosyl-α1-4-galactose (Galα1-4Gal)-containing host receptors. A functionally unknown S. suis cell wall protein (SSU0253), designated here as SadP (streptococcal adhesin P), was identified using a Galα1-4Gal-containing affinity matrix and LC-ESI mass spectrometry. Although the function of the protein was not previously known, it was recently identified as an immunogenic cell wall protein in a proteomic study. Insertional inactivation of the sadP gene abolished S. suis Galα1-4Gal-dependent binding. The adhesin gene sadP was cloned and expressed in Escherichia coli. Characterization of its binding specificity showed that SadP recognizes Galα1-4Gal-oligosaccharides and binds its natural glycolipid receptor, GbO(3) (CD77). The N terminus of SadP was shown to contain a Galα1-Gal-binding site and not to have apparent sequence similarity to other bacterial adhesins, including the E. coli P fimbrial adhesins, or to E. coli verotoxin or Pseudomonas aeruginosa lectin I also recognizing the same Galα1-4Gal disaccharide. The SadP and E. coli P adhesins represent a unique example of convergent evolution toward binding to the same host receptor structure.
authors: Department of Medical Biochemistry and Genetics, University of Turku, Kiinamyllynkatu 10, Turku FI-20520, Finland.
authors: Annika
authors: A
authors: Kouki
authors: Sauli
authors: S
authors: Haataja
authors: Vuokko
authors: V
authors: Loimaranta
authors: Arto T
authors: AT
authors: Pulliainen
authors: Ulf J
authors: UJ
authors: Nilsson
authors: Jukka
authors: J
authors: Finne
mesh_terms: D018829:Adhesins, Bacterial / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000818:Animals; D003001:Cloning, Molecular; D004187:Disaccharides / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019143:Evolution, Molecular; D015870:Gene Expression; D006023:Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006801:Humans; D013058:Mass Spectrometry; D009154:Mutation; D011485:Protein Binding; D040901:Proteomics; D017011:Streptococcus suis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013552:Swine; D013553:Swine Diseases; D014281:Trihexosylceramides / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D018829:Adhesins, Bacterial; D004187:Disaccharides; D006023:Glycoproteins; D014281:Trihexosylceramides; C032103:4-O-alpha-D-galactopyranosyl-D-galactose; C018549:globotriaosylceramide