Adhesion determinants of the Streptococcus species.
Bottom Line: Phylogenetic analyses based on 16S rRNA sequences of the streptococcal species reveal a clustering pattern, reflecting, with a few exceptions, their pathogenic potential and ecological preferences.Bacterial adhesins recognize and bind cell surface molecules and extracellular matrix components through specific domains that for certain adhesin families have been well defined and found conserved across the streptococcal species.In this review, we present the different streptococcal adhesin families categorized on the basis of their adhesive properties and structural characteristics, and, when available, we focus the attention on conserved functional domains.
Affiliation: Novartis Vaccines and Diagnostics, Via Fiorentina 1, Siena, Italy.Show MeSH
Related in: MedlinePlus
Mentions: An important ubiquitous extracellular host protein targeted by a variety of streptococcal adhesins is Fn. The interaction is mediated by bacterial Fn binding proteins (FnBPs) that belong to the MSCRAMM family of adhesins (Patti et al., 1994). FnBPs in streptococci have a similar molecular organization, although the sequence length can vary considerably. They all contain an N‐terminal signal sequence, a C‐terminal cell wall LPXTG‐anchoring motif and a short positively charged C‐terminal tail (Schwarz‐Linek et al., 2006). The Fn binding activity is located in the C‐terminal half of the molecule, where sequence repeats of 30–40 residues can be found (Fn binding repeats, FnBRs); FnBRs target the N‐terminal domain (NTD) of Fn (Fig. 2A). In addition, some proteins contain an upstream Fn binding domain. Interestingly, FnBRs are intrinsically disordered regions within FnBPs. They were shown to adopt a more ordered conformation upon binding to the NTD of Fn (House‐Pompeo et al., 1996), thus defining a novel type of protein–protein interaction named ‘tandem β‐zipper’ (Schwarz‐Linek et al., 2003). Each of the repeats can potentially bind to an Fn dimer, which contains two RGD binding sites for integrins. Fibronectin, in this model of interaction, functions as a molecular bridge between the bacteria and the host cell integrins in the FnBP‐mediated bacteria internalization (Ozeri et al., 1998). It is not clear if the number of FnBRs in FnBPs is correlated to adhesion or to invasion efficiency.
Affiliation: Novartis Vaccines and Diagnostics, Via Fiorentina 1, Siena, Italy.