Structural and Functional Analysis of the N-terminal Domain of the Streptococcus gordonii Adhesin Sgo0707

Åsa Nylander,Dennis G Cvitkovitch,Dilani B Senadheera,Karina Persson,Julia R Davies,Gunnel Svensäter

doi:10.1371/journal.pone.0063768

Åsa Nylander, Dennis G Cvitkovitch + Show 4 more

Open Access

https://doi.org/10.1371/journal.pone.0063768

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Journal: PloS one	Publication Date: May 17, 2013
Citations: 13	License type: CC BY 4.0

Affiliation: Umeå University, University of Toronto, Malmö University

Abstract

The commensal Streptococcus gordonii expresses numerous surface adhesins with which it interacts with other microorganisms, host cells and salivary proteins to initiate dental plaque formation. However, this Gram-positive bacterium can also spread to non-oral sites such as the heart valves and cause infective endocarditis. One of its surface adhesins, Sgo0707, is a large protein composed of a non-repetitive N-terminal region followed by several C-terminal repeat domains and a cell wall sorting motif. Here we present the crystal structure of the Sgo0707 N-terminal domains, refined to 2.1 Å resolution. The model consists of two domains, N1 and N2. The largest domain, N1, comprises a putative binding cleft with a single cysteine located in its centre and exhibits an unexpected structural similarity to the variable domains of the streptococcal Antigen I/II adhesins. The N2-domain has an IgG-like fold commonly found among Gram-positive surface adhesins. Binding studies performed on S. gordonii wild-type and a Sgo0707 deficient mutant show that the Sgo0707 adhesin is involved in binding to type-1 collagen and to oral keratinocytes.

Highlights

Oral streptococci are the most abundant bacteria in the oral cavity and approximately 70% of early colonizers belong to the streptococcal family [1]
The commensal strain Streptococcus gordonii expresses an array of surface adhesins, for example the Antigen I/ II (AgI/II) proteins SspA and SspB, and CshA and CshB that mediate interactions with salivary agglutinin [3,4]
S. gordonii is mainly beneficial for oral health, the bacteria can become pathogenic if they spread to non-oral sites such as the heart valves with infective endocarditis as the result [9]

Summary

Introduction

Oral streptococci are the most abundant bacteria in the oral cavity and approximately 70% of early colonizers belong to the streptococcal family [1]. Colonization occurs through bacterial adherence to molecules in the saliva-derived pellicle which covers all surfaces in the oral cavity. The salivary pellicle contains proteins, peptides and other molecules and so far 130 proteins have been identified [2]. The bacteria utilize a variety of cell surface proteins in order to adhere to a surface and thereby avoid clearance through swallowing. The commensal strain Streptococcus gordonii expresses an array of surface adhesins, for example the Antigen I/ II (AgI/II) proteins SspA and SspB, and CshA and CshB that mediate interactions with salivary agglutinin (gp340) [3,4]. S. gordonii is mainly beneficial for oral health, the bacteria can become pathogenic if they spread to non-oral sites such as the heart valves with infective endocarditis as the result [9]

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