Identification and expression of a gene encoding for sialidase from Streptococcus oralis C104
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S. oralis is a member of the normal oral flora and an opportunistic pathogen in patient with attenuated host defensive mechanisms. The mechanisms by which S. oralis causes this wide range of infections are as yet unclear, but the sialidase produced by this organism has been proposed as a contributing factor. The precise role of these enzymes is unknown, but it has been suggested that they act as generalized virulence determinants in that the release of sialic acid may expose cryptic carbohydrate binding sites for the invading organisms and break down mucosal defensive barriers of the host. In order to explore the role of this enzyme, a gene encoding for sialidase was cloned from S. oralis Cl 04. A phagemid expressing sialidase activity containing a DNA insert of 4.7 kb was completely sequenced. This insert contained the complete sialidase gene and two incomplete ORFs. The sialidase gene is homologous to sialidases from a variety of bacteria including S. pneumoniae, Erysipelothrix rhusiopathiae, and Clostridium per:fingens. The sialidase gene contained four aspartate boxes (S-X-D-X-G-X-T-W) and an anchor motif (L-P-N-T-G-S) at the C-terminus end. The anchor motif allows the protein to cross the cell wall and anchors it to the cell surface. An incomplete ORF was found 327 bp upstream of the sialidase · gene. It was homologous to an acetylxylan esterase gene on a number of bacterial species including S. pneumoniae and Bacillus halodurans. Another incomplete ORF was found 249 hp downstream of the sialidase gene. It was homologous to the putative N-acetylmannosarnine-6-phosphate epimerase from a number of bacterial species including S. pneumoniae nanE and Streptococcus pyogene. [TRUNCATED]
PLEASE NOTE: This work is protected by copyright. Downloading is restricted to the BU community: please click Download and log in with a valid BU account to access. If you are the author of this work and would like to make it publicly available, please contact email@example.com.Thesis (M.Sc.D)--Boston University, Henry M. Goldman School of Dental Medicine, 2001 (Pediatric Dentistry).
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