title: Isolation and characterisation of sialidase from a strain of Streptococcus oralis.
abstract: Streptococcus oralis, the most virulent of the viridans streptococci, produces a sialidase and this exo-glycosidase has been implicated in the disease process of a number of pathogens. The sialidase of S. oralis strain AR3 was purified in order to understand the characteristics of this putative virulence determinant. The enzyme isolated as a high mol. wt aggregate (c. 325 kDa) was purified 4520-fold from late exponential phase cultures by a combination of ultrafiltration, ammonium sulphate precipitation, ion-exchange and gel filtration chromatography. The sialidase component had a mol.wt of 144 kDa as determined by SDS-PAGE analysis. The purified sialidase released N-acetylneuraminic acid from a range of sialoglycoconjugates including human alpha1-acid glycoprotein, bovine submaxillary mucin, colominic acid and sialyl-alpha2,3- and sialyl-alpha2,6-lactose. Also, N-glycolylneuraminic acid was cleaved from bovine submaxillary mucin. The sialidase had a Km of 11.8 microM for alpha1-acid glycoprotein, was active over a broad pH range with a pH optimum of 6.0 and cleaved alpha2,3-, alpha2,6- and alpha2-8-sialyl glycosidic linkages with a marked preference for alpha2,3-linkages. The enzyme was competitively inhibited by the sialic acid derivative, 2,3-dehydro-N-acetylneuraminic acid, with a K(IC) of 1.2 microM. The characteristics of the purified sialidase would support a nutritional role for this enzyme that may be significant in the proliferation of this organism in the oral cavity and at extra-oral sites in association with life-threatening infections.
authors.affiliation: Joint Microbiology Research Unit, GKT Dental Institute, London SE5 9RW.
authors.forename: H L
authors.initials: HL
authors.lastname: Byers
authors.affiliation: Joint Microbiology Research Unit, GKT Dental Institute, London SE5 9RW.
authors.forename: E
authors.initials: E
authors.lastname: Tarelli
authors.affiliation: Joint Microbiology Research Unit, GKT Dental Institute, London SE5 9RW.
authors.forename: K A
authors.initials: KA
authors.lastname: Homer
authors.affiliation: Joint Microbiology Research Unit, GKT Dental Institute, London SE5 9RW.
authors.forename: D
authors.initials: D
authors.lastname: Beighton
mesh_terms: D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007700:Kinetics; D008970:Molecular Weight; D009439:Neuraminidase / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism; D012795:Sialoglycoproteins / Q000378:metabolism; D019533:Streptococcus oralis / Q000201:enzymology* / Q000472:pathogenicity; D013379:Substrate Specificity; D014462:Ultrafiltration; D014774:Virulence
chemical_list: D012795:Sialoglycoproteins; D009439:Neuraminidase