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Crystal structure of the variable domain of the Streptococcus gordonii surface protein SspB
Umeå University, Faculty of Medicine, Department of Odontology, Cariology. (Karina Persson)
Umeå University, Faculty of Medicine, Department of Odontology, Cariology. (Karina Persson)
2009 (English)In: Protein Science, ISSN 0961-8368, Vol. 18, no 9, 1896-1905 p.Article in journal (Refereed) Published
Abstract [en]

The Antigen I/II (AgI/II) family of proteins are cell wall anchored adhesins expressed on the surface of oral streptococci. The AgI/II proteins interact with molecules on other bacteria, on the surface of host cells, and with salivary proteins. Streptococcus gordonii is a commensal bacterium, and one of the primary colonizers that initiate the formation of the oral biofilm. S. gordonii expresses two AgI/II proteins, SspA and SspB that are closely related. One of the domains of SspB, called the variable (V-) domain, is significantly different from corresponding domains in SspA and all other AgI/II proteins. As a first step to elucidate the differences among these proteins, we have determined the crystal structure of the V-domain from S. gordonii SspB at 2.3 A resolution. The domain comprises a beta-supersandwich with a putative binding cleft stabilized by a metal ion. The overall structure of the SspB V-domain is similar to the previously reported V-domain of the Streptococcus mutans protein SpaP, despite their low sequence similarity. In spite of the conserved architecture of the binding cleft, the cavity is significantly smaller in SspB, which may provide clues about the difference in ligand specificity. We also verified that the metal in the binding cleft is a calcium ion, in concurrence with previous biological data. It was previously suggested that AgI/II V-domains are carbohydrate binding. However, we tested that hypothesis by screening the SspB V-domain for binding to over 400 glycoconjucates and found that the domain does not interact with any of the carbohydrates.

Place, publisher, year, edition, pages
2009. Vol. 18, no 9, 1896-1905 p.
Keyword [en]
crystal structure, protein structure, oral biofilm, surface adhesin
National Category
Biochemistry and Molecular Biology Structural Biology
Research subject
Biochemistry; Odontology
URN: urn:nbn:se:umu:diva-25828DOI: 10.1002/pro.200PubMedID: 19609934OAI: diva2:234110
Available from: 2009-09-04 Created: 2009-09-04 Last updated: 2011-09-10
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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