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author:("Shi, wenchuan")
1.  Effects on Hardness and Elastic Modulus for DSS-8 Peptide Treatment on Remineralization of Human Dental Tissues 
Dental remineralization may be achieved by mediating the interactions between tooth surfaces with free ions and biomimetic peptides. We recently developed octuplet repeats of aspartate-serine-serine (DSS-8) peptide, which occurs in high abundance in naturally occurring proteins that are critical for tooth remineralization. In this paper, we evaluated the possible role of DSS-8 in enamel remineralization. Human enamel specimens were demineralized, exposed briefly to DSS-8 solution, and then exposed to concentrated ionic solutions that favor remineralization. Enamel nano-mechanical behaviors, hardness and elastic modulus, at various stages of treatment were determined by nanoindentation. The phase, microstructure and morphology of the resultant surfaces were characterized using the grazing incidence X-ray diffraction (GIXD), variable pressure scanning electron microscopy (VPSEM), and atomic force microscopy (AFM), respectively. Nanoindentation results show that the DSS-8 remineralization effectively improves the mechanical and elastic properties for demineralized enamel.
doi:10.1557/PROC-1132-Z09-05
PMCID: PMC4209483  PMID: 25355990
Enamel; Peptide; Nanoindentation; Remineralization
2.  The cia Operon of Streptococcus mutans Encodes a Unique Component Required for Calcium-Mediated Autoregulation 
Molecular microbiology  2008;70(1):112-126.
Streptococcus mutans is a primary pathogen for dental caries in humans. CiaR and CiaH of S. mutans comprise a two-component signal transduction system (TCS) involved in regulating various virulent factors. However, the signal that triggers the CiaRH response remains unknown. In this study, we show that calcium is a signal for regulation of the ciaRH operon, and that a double-glycine-containing small peptide encoded within the ciaRH operon (renamed ciaX) mediates this regulation. CiaX contains a serine-aspartate (SD) domain that is shared by calcium-binding proteins. A markerless in-frame deletion of ciaX reduced ciaRH operon expression and diminished the calcium repression of operon transcription. Point mutations of the SD-domain resulted in the same phenotype as the in-frame deletion, indicating that the SD-domain is required for CiaX function. Further characterization of ciaX demonstrated that it is involved in calcium mediated biofilm formation. Furthermore, inactivation of ciaR or ciaH led to the same phenotype as the in-frame deletion of ciaX, suggesting that all three genes are involved in the same regulatory pathway. Sequence analysis and real-time RT-PCR identified a putative CiaR binding site upstream of ciaX. We conclude that the ciaXRH operon is a three-component, self-regulatory system modulating cellular functions in response to calcium.
doi:10.1111/j.1365-2958.2008.06390.x
PMCID: PMC2955730  PMID: 18681938
3.  The Fusobacterium nucleatum Outer Membrane Protein RadD Is an Arginine-Inhibitable Adhesin Required for Inter-Species Adherence and the Structured Architecture of Multi-Species Biofilm 
Molecular microbiology  2008;71(1):35-47.
Summary
A defining characteristic of the suspected periodontal pathogen Fusobacterium nucleatum is its ability to adhere to a plethora of oral bacteria. This distinguishing feature is suggested to play an important role in oral biofilm formation and pathogenesis, with fusobacteria proposed to serve as central “bridging organisms” in the architecture of the oral biofilm bringing together species which would not interact otherwise. Previous studies indicate that these bacterial interactions are mediated by galactose- or arginine-inhibitable adhesins although genetic evidence for the role and nature of these proposed adhesins remains elusive. To characterize these adhesins at the molecular level, the genetically transformable F. nucleatum strain ATCC 23726 was screened for adherence properties, and arginine inhibitable adhesion was evident, while galactose-inhibitable adhesion was not detected. Six potential arginine binding proteins were isolated from the membrane fraction of F. nucleatum ATCC 23726 and identified via mass spectroscopy as members of the outer membrane family of proteins in F. nucleatum. Inactivation of the genes encoding these six candidates for arginine-inhibitable adhesion and two additional homologues revealed that only a mutant derivative carrying an insertion in Fn1526 (now designated as radD) demonstrated significantly decreased co-aggregation with representatives of the Gram-positive “early oral colonizers”. Lack of the 350 kDa outer membrane protein encoded by radD resulted in the failure to form the extensive structured biofilm observed with the parent strain when grown in the presence of Streptococcus sanguinis ATCC 10556. These findings indicate that radD is responsible for arginine-inhibitable adherence of F. nucleatum and provides definitive molecular evidence that F. nucleatum adhesins play a vital role in inter-species adherence and multispecies biofilm formation.
doi:10.1111/j.1365-2958.2008.06503.x
PMCID: PMC2741168  PMID: 19007407
Fusobacterium nucleatum; RadD. Arginine; Adhesin; Biofilm; Co-aggregation
4.  SO-LAAO, a Novel l-Amino Acid Oxidase That Enables Streptococcus oligofermentans To Outcompete Streptococcus mutans by Generating H2O2 from Peptone▿ † 
Journal of Bacteriology  2008;190(13):4716-4721.
We previously demonstrated that Streptococcus oligofermentans suppressed the growth of Streptococcus mutans, the primary cariogenic pathogen, by producing hydrogen peroxide (H2O2) through lactate oxidase activity. In this study, we found that the lox mutant of S. oligofermentans regained the inhibition while growing on peptone-rich plates. Further studies demonstrated that the H2O2 produced on peptone by S. oligofermentans was mainly derived from seven l-amino acids, i.e., l-aspartic acid, l-tryptophan, l-lysine, l-isoleucine, l-arginine, l-asparagine, and l-glutamine, indicating the possible existence of l-amino acid oxidase (LAAO) that can produce H2O2 from l-amino acids. Through searching the S. oligofermentans genome for open reading frames with a conserved flavin adenine dinucleotide binding motif that exists in the known LAAOs, including those of snake venom, fungi, and bacteria, a putative LAAO gene, assigned as aaoSo, was cloned and overexpressed in Escherichia coli. The purified protein, SO-LAAO, showed a molecular mass of 43 kDa in sodium dodecyl sulfate-polyacrylamide gel electrophoresis and catalyzed H2O2 formation from the seven l-amino acids determined above, thus confirming its LAAO activity. The SO-LAAO identified in S. oligofermentans differed evidently from the known LAAOs in both substrate profile and sequence, suggesting that it could represent a novel LAAO. An aaoSo mutant of S. oligofermentans did lose H2O2 formation from the seven l-amino acids, further verifying its function as an LAAO. Furthermore, the inhibition by S. oligofermentans of S. mutans in a peptone-rich mixed-species biofilm was greatly reduced for the aaoSo mutant, indicating the gene's importance in interspecies competition.
doi:10.1128/JB.00363-08
PMCID: PMC2446784  PMID: 18469105

Results 1-4 (4)