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Two intramolecular isopeptide bonds are identified in the crystal structure of the Streptococcus gordonii SspB c-terminal domain
Umeå University, Faculty of Medicine, Department of Odontology, Cariology. (Karina Persson)
Umeå University, Faculty of Medicine, Department of Odontology, Cariology.
2010 (English)In: Journal of Molecular Biology, ISSN 0022-2836, E-ISSN 1089-8638, Vol. 397, no 3, 740-751 p.Article in journal (Refereed) Published
Abstract [en]

Streptococcus gordonii is a primary colonizer and is involved in the formation of dental plaque. This bacterium expresses several surface proteins. One of them is the adhesin SspB, which is a member of the Antigen I/II family of proteins. SspB is a large multi-domain protein that has interactions with surface molecules on other bacteria and on host cells, and is thus a key factor in the formation of biofilms. Here, we report the crystal structure of a truncated form of the SspB C-terminal domain, solved by single-wavelength anomalous dispersion to 1.5Å resolution. The structure represents the first of a C-terminal domain from a streptococcal Antigen I/II protein and is comprised of two structurally related β-sandwich domains, C2 and C3, both with a Ca2+ bound in equivalent positions. In each of the domains, a covalent isopeptide bond is observed between a lysine and an asparagine, a feature that is believed to be a common stabilization mechanism in Gram-positive surface proteins. S. gordonii biofilms contain attachment sites for the periodontal pathogen Porphyromonas gingivalis and the SspB C-terminal domain has been shown to have one such recognition motif, the SspB adherence region. The motif protrudes from the protein, and serves as a handle for attachment. The structure suggests several additional putative binding surfaces, and other binding clefts may be created when the fulllength protein is folded.

Place, publisher, year, edition, pages
Academic Press, 2010. Vol. 397, no 3, 740-751 p.
Keyword [en]
crystal structure, X-ray crystallography, protein structure, surface adhesin, isopeptide bond
National Category
Dentistry Structural Biology Medical Biotechnology (with a focus on Cell Biology (including Stem Cell Biology), Molecular Biology, Microbiology, Biochemistry or Biopharmacy)
Research subject
Biochemistry; Odontology
URN: urn:nbn:se:umu:diva-32907DOI: 10.1016/j.jmb.2010.01.065ISI: 000276177300010PubMedID: 20138058OAI: diva2:306651
Available from: 2010-03-30 Created: 2010-03-30 Last updated: 2015-12-29Bibliographically approved
In thesis
1. Structural studies of the surface adhesin SspB from Streptococcus gordonii
Open this publication in new window or tab >>Structural studies of the surface adhesin SspB from Streptococcus gordonii
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Surface proteins on microorganisms that build up the oral biofilm are key players in the formation of the biofilm. Antigen I/II proteins are surface adhesins found on virtually all oral streptococci and share a conserved multi-domain architecture. These adhesins bind surface components on other bacteria and on host cells. Thus, they are crucial for the development of the biofilm.    

The objective of this thesis work is the structural characterization of the large multi-domain Antigen I/II protein SspB from the primary colonizing commensal bacterium Streptococcus gordonii.

The crystal structure of the variable domain of SspB was determined to 2.3 Å resolution. The domain comprises a β-supersandwich and a putative binding cleft stabilized by a calcium ion. Despite high similarity in the overall structure, the cleft within SspB is significantly smaller than the cleft within the homologous protein from Streptococcus mutans, indicating that different substrates may bind in the clefts. A screen for carbohydrate binding resulted in no hits for interaction with the SspB variable domain suggesting that the cleft may not be suitable for binding sugars.

This thesis also presents the high resolution 1.5 Å structure of a truncated C-terminal domain of SspB, the first of an Antigen I/II C-domain. The structure contains two structurally related domains, each containing one calcium ion and one intramolecular isopeptide bond. The SspB protein shares the feature of intramoleular isopeptide bonds with other surface proteins from Gram positive bacteria, such as pili from Streptococcus pyogenes and Corynebacterium diphtheriae. Intramolecular isopeptide bonds are suggested to be a common feature for retaining stability in a harsh environment. The SspB adherence region, shown to be the recognition motif for Porphyromonas gingivalis attachment to S. gordonii, protrudes from the core protein as a handle available for recognition.

In conclusion, this thesis work has provided new knowledge about the SspB protein and increased the understanding of the common structure of AgI/II proteins.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2010. 41 p.
Umeå University odontological dissertations, ISSN 0345-7532 ; 111
Streptococcus gordonii, X-ray crystallography, surface adhesin, dental plaque, structural biology
National Category
Structural Biology Dentistry
Research subject
urn:nbn:se:umu:diva-32910 (URN)978-91-7264-955-2 (ISBN)
Public defence
2010-04-23, Sal D, By 1D, Tandläkarhögskolan, NUS, Umeå, 13:00 (English)
Available from: 2010-04-01 Created: 2010-03-30 Last updated: 2010-04-01Bibliographically approved

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