title: Crystal structure of glucansucrase from the dental caries pathogen Streptococcus mutans.
abstract: Glucansucrase (GSase) from Streptococcus mutans is an essential agent in dental caries pathogenesis. Here, we report the crystal structure of S. mutans glycosyltransferase (GTF-SI), which synthesizes soluble and insoluble glucans and is a glycoside hydrolase (GH) family 70 GSase in the free enzyme form and in complex with acarbose and maltose. Resolution of the GTF-SI structure confirmed that the domain order of GTF-SI is circularly permuted as compared to that of GH family 13 α-amylases. As a result, domains A, B and IV of GTF-SI are each composed of two separate polypeptide chains. Structural comparison of GTF-SI and amylosucrase, which is closely related to GH family 13 amylases, indicated that the two enzymes share a similar transglycosylation mechanism via a glycosyl-enzyme intermediate in subsite -1. On the other hand, novel structural features were revealed in subsites +1 and +2 of GTF-SI. Trp517 provided the platform for glycosyl acceptor binding, while Tyr430, Asn481 and Ser589, which are conserved in family 70 enzymes but not in family 13 enzymes, comprised subsite +1. Based on the structure of GTF-SI and amino acid comparison of GTF-SI, GTF-I and GTF-S, Asp593 in GTF-SI appeared to be the most critical point for acceptor sugar orientation, influencing the transglycosylation specificity of GSases, that is, whether they produced insoluble glucan with α(1-3) glycosidic linkages or soluble glucan with α(1-6) linkages. The structural information derived from the current study should be extremely useful in the design of novel inhibitors that prevent the biofilm formation by GTF-SI.
authors.affiliation: Department of Food and Nutritional Sciences, Graduate School of Nutritional and Environmental Sciences, University of Shizuoka, 52-1 Yada, Suruga-Ku, Shizuoka 422-8526, Japan. itosohei@u-shizuoka-ken.ac.jp
authors.forename: Keisuke
authors.initials: K
authors.lastname: Ito
authors.forename: Sohei
authors.initials: S
authors.lastname: Ito
authors.forename: Tatsuro
authors.initials: T
authors.lastname: Shimamura
authors.forename: Simone
authors.initials: S
authors.lastname: Weyand
authors.forename: Yasuaki
authors.initials: Y
authors.lastname: Kawarasaki
authors.forename: Takumi
authors.initials: T
authors.lastname: Misaka
authors.forename: Keiko
authors.initials: K
authors.lastname: Abe
authors.forename: Takuya
authors.initials: T
authors.lastname: Kobayashi
authors.forename: Alexander D
authors.initials: AD
authors.lastname: Cameron
authors.forename: So
authors.initials: S
authors.lastname: Iwata
mesh_terms: D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D003731:Dental Caries / Q000201:enzymology* / Q000382:microbiology / Q000473:pathology; D005936:Glucans / Q000378:metabolism; D005964:Glucosyltransferases / Q000737:chemistry / Q000378:metabolism; D006031:Glycosylation; D016695:Glycosyltransferases / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D013295:Streptococcus mutans / Q000201:enzymology*
chemical_list: D005936:Glucans; D016695:Glycosyltransferases; D005964:Glucosyltransferases; C033837:alternansucrase; C019700:amylosucrase