is closely associated with the pathogenesis of dental caries (Hamada & Slade, 1980
). The mechanism of dental caries involves the initial formation of a biofilm, or dental plaque, comprised of a sticky glucose polymer (glucan) that is produced by S. mutans
in which oral bacteria, food debris and salivary components can become trapped. Acids derived from the fermentation of dietary carbohydrates such as sucrose, fructose and glucose lead to the demineralization of the adjacent tooth surface and ultimately to dental caries. Sticky glucan plays an essential role in the aetiology and pathogenesis of dental caries (Yamashita et al.
). Dental plaques also cause co-pathologies such as infection, periodontal disease and halitosis (Liu et al.
). Sticky glucan is synthesized from sucrose by glucansucrases (GSases) encoded by S. mutans
. Therefore, these enzymes are attractive drug targets for the development of effective treatments for dental caries (Newbrun et al.
). Several inhibitors of GSases from S. mutans
have been identified that can prevent dental caries (Yanagida et al.
; Koo et al.
). Detailed structural information on GSases would be instrumental in the development of more effective treatments; however, to date crystallographic structural analyses of S. mutans
GSases have yet to be reported.
GSase is a glycosyl transferase (GTF) and a member of glycoside hydrolase family 70 (GH 70; http://afmb.cnrs-mrs.fr/CAZY/
). GSase is a large enzyme, with an average molecular weight of 160 kDa. GSases contain an N-terminal variable region, a conserved catalytic domain of approximately 900 amino acids and a C-terminal domain of approximately 500 amino acids composed of a series of homologous directly repeating units that are responsible for glucan binding (Monchois et al.
). The regions of GSase that are essential for enzyme catalysis have been precisely identified (Monchois et al.
; van Hijum et al.
), but the detailed mechanisms of regioselectivity and stereospecificity remain unclear.
In the oral cavity, sticky glucan synthesis by S. mutans
is mediated by three extracellular GSases: GTF-SI, GTF-I and GTF-S (Tamesada et al.
). GTF-SI and GTF-I are mainly involved in the synthesis of insoluble glucan containing α(1–3) glycosidic linkages, while GTF-S is primarily involved in the synthesis of soluble α(1–6)-linked glucan (Monchois et al.
; van Hijum et al.
). Together, these three enzymes function cooperatively to produce insoluble sticky glucan.
Here, we present a crystallization report for the GSase GTF-SI from the dental caries pathogen S. mutans, including a description of the expression, purification, crystallization and preliminary X-ray analysis of GTF-SI.