Summary auto-generated
Researchers isolated and characterized a sialidase enzyme from Streptococcus oralis strain AR3, a virulent viridans streptococcus associated with infective endocarditis and serious infections in immunocompromised patients. The enzyme was purified 4520-fold from bacterial culture supernatant using ultracentrifugation, ammonium sulfate precipitation, ion-exchange, and gel filtration chromatography. The sialidase exists as a high molecular weight aggregate (~325 kDa) containing a 144 kDa enzymatic component. The purified enzyme cleaved N-acetylneuraminic acid and N-glycolylneuraminic acid from various sialoglycoconjugates including glycoproteins and oligosaccharides. It showed broad substrate specificity for α2,3-, α2,6-, and α2,8-linked sialyl residues, with preference for α2,3-linkages. The enzyme had a Km of 11.8 μM for human α1-acid glycoprotein, a pH optimum of 6.0, and was competitively inhibited by 2,3-dehydro-N-acetylneuraminic acid. These characteristics support a nutritional role for sialidase in bacterial proliferation, potentially enabling growth on host glycoproteins in oral and extraoral sites.
Key findings
- S. oralis sialidase was purified 4520-fold and exists as a 144 kDa enzyme within a higher molecular weight complex
- The enzyme broadly cleaves sialic acids from multiple glycoconjugates with preference for α2,3-linked residues and optimal activity at pH 6.0
- Sialidase has a low Km (11.8 μM) for human α1-acid glycoprotein, indicating high affinity for complex N-linked glycoproteins
- The enzyme is competitively inhibited by 2,3-dehydro-N-acetylneuraminic acid, confirming its role in sialic acid metabolism
- Sialidase characteristics suggest it enables S. oralis to utilize host glycoproteins as fermentable carbohydrate sources for growth
This summary was generated automatically from the article PDF and is not part of the original publication. Refer to the PDF for the authoritative text.
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 α1-acid glycoprotein, bovine submaxillary mucin, colominic acid and sialyl-α2,3- and sialyl-α2,6-lactose. Also, N-glycolylneuraminic acid was cleaved from bovine submaxillary mucin. The sialidase had a Km of 11.8 µM for α1-acid glycoprotein, was active over a broad pH range with a pH optimum of 6.0 and cleaved α2,3-, α2,6- and α2-8-sialyl glycosidic linkages with a marked preference for α2,3-linkages. The enzyme was competitively inhibited by the sialic acid derivative, 2,3-dehydro-N-acetylneuraminic acid, with a KIC of 1.2 µm. 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.