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Journal of Bacteriology, January 2009, p. 394-402, Vol. 191, No. 1
0021-9193/09/$08.00+0     doi:10.1128/JB.00838-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Streptococcus mutans SMU.623c Codes for a Functional, Metal-Dependent Polysaccharide Deacetylase That Modulates Interactions with Salivary Agglutinin{triangledown} ,{dagger}

Dong Mei Deng,1* Jonathan E. Urch,2 Jacob M. ten Cate,1 Vincenzo A. Rao,2 Daan M. F. van Aalten,2 and Wim Crielaard1,3

Department of Cariology Endodontology Pedodontology, Academic Centre for Dentistry Amsterdam (ACTA), Amsterdam 1066 EA, The Netherlands,1 Division of Biological Chemistry and Drug Discovery, School of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom,2 Swammerdam Institute for Life Sciences (SILS), University of Amsterdam, Amsterdam 1018 WV, The Netherlands3

Received 17 June 2008/ Accepted 21 October 2008

The genome sequence of the oral pathogen Streptococcus mutans predicts the presence of two putative polysaccharide deacetylases. The first, designated PgdA in this paper, shows homology to the catalytic domains of peptidoglycan deacetylases from Streptococcus pneumoniae and Listeria monocytogenes, which are both thought to be involved in the bacterial defense mechanism against human mucosal lysozyme and are part of the CAZY family 4 carbohydrate esterases. S. mutans cells in which the pgdA gene was deleted displayed a different colony texture and a slightly increased cell surface hydrophobicity and yet did not become hypersensitive to lysozyme as shown previously for S. pneumoniae. To understand this apparent lack of activity, the high-resolution X-ray structure of S. mutans PgdA was determined; it showed the typical carbohydrate esterase 4 fold, with metal bound in a His-His-Asp triad. Analysis of the protein surface showed that an extended groove lined with aromatic residues is orientated toward the active-site residues. The protein exhibited metal-dependent de-N-acetylase activity toward a hexamer of N-acetylglucosamine. No activity was observed toward shorter chitooligosaccharides or a synthetic peptidoglycan tetrasaccharide. In agreement with the lysozyme data this would suggest that S. mutans PgdA does not act on peptidoglycan but on an as-yet-unidentified polysaccharide within the bacterial cell surface. Strikingly, the pgdA-knockout strain showed a significant increase in aggregation/agglutination by salivary agglutinin, in agreement with this gene acting as a deacetylase of a cell surface glycan.

* Corresponding author. Mailing address: Department of Cariology Endodontology Pedodontology, ACTA, Louwesweg 1, 1066 EA Amsterdam, The Netherlands. Phone: 31 20 5188432. Fax: 31 20 6692881. E-mail: d.deng{at}acta.nl

{triangledown} Published ahead of print on 31 October 2008.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, January 2009, p. 394-402, Vol. 191, No. 1
0021-9193/09/$08.00+0     doi:10.1128/JB.00838-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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