Graduation Year

2004

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Biology

Major Professor

Dao, My Lien.

Keywords

Dental root decay, Collagen, U32 peptidase, Metalloproteinase, Gelatinase

Abstract

Streptococcus mutans is a recognized principal etiologic agent in coronal caries. Although S. mutans has the ability to bind collagen and degrade FALGPA, a synthetic peptide mimicking collagen substrate, its role in dental root caries has not yet been fully elucidated. Degradation of collagen fibrils in dentin was attributed to S. mutans, but a collagenase enzyme has not yet been isolated from this organism. Considering the increased incidence of dental root decay among the elderly, an understanding of the role of the pathogenic factors is necessary to the development of preventive measures. The present study has focused on the cloning and analysis of S. mutans collagenase enzyme. Toward this goal, a putative collagenase gene was identified in S. mutans UA159 by genomic analysis and a primer set was designed and used to amplify the corresponding gene in S. mutans GS-5 used as a model organism.

The PCR product was cloned into the vector pCR 2.1 TOPO-TA, and the gene sequenced and analyzed. Alignment of the S. mutans GS-5 and UA159 putative collagenase genes showed 99% homology. The gene was next cloned in frame into the inducible expression vector pET100/D TOPO. Induction and expression of recombinant protein in E. coli were confirmed by SDS-PAGE and Western immunoblotting, while biochemical analysis indicated that it was a calcium- dependent metalloproteinase. Enzyme analysis of the recombinant enzyme showed both gelatinolytic and collagenolytic activity. Further analysis of the GS-5 gene using databases such as ExPASy, Pfam, and SMART indicated that it was highly homologous to the U32 peptidase family, which includes the PrtC collagenase of Porphyromonas gingivalis, a bacterium causing periodontitis. The present study was the first to unequivocally demonstrate the existence of a collagenase gene in S.

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