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Biomaterial, Host, and Microbial Interactions
Published in Mary Anne S. Melo, Designing Bioactive Polymeric Materials for Restorative Dentistry, 2020
Glucosyltransferase (gtf) genes have been found to encode glucosyltransferase enzymes in S. mutans, which are responsible for the synthesis of glucans and function in bacterial attachment and biofilm formation on the surface of teeth (Khalichi et al. 2009). Singh et al. (2009) showed that both Bis-HPPP and MA upregulated glucosyltransferase B (gtfB) gene expression in S. mutans NG8 cells. It is believed that the elevated levels of these BBPs create environmental stress that stimulates a bacterial response that promotes the transcription of genes needed for glucan production (Jefferson 2004). In addition to an increased ability for bacterial adhesion and biofilm formation, another bacterial response to BBPs is enhanced SMU_118c gene expression. SMU_118c is a dominant esterase from S. mutans capable of hydrolyzing the constitutive monomers of composite resin, and therefore increased SMU_118c esterase production may accelerate the biodegradation of the resin-dentin interface, ultimately contributing to the failure of resin composite restorations (Huang, Sadeghinejad et al. 2018).
Biosynthesis and Genetics of Lipopolysaccharide Core
Published in Helmut Brade, Steven M. Opal, Stefanie N. Vogel, David C. Morrison, Endotoxin in Health and Disease, 2020
David E. Heinrichs, Chris Whitfield, Miguel A. Valvano
In the first molecular-genetic studies on LPS core OS assembly, a Salmonella waaG mutant was functionally complemented with plasmids containing E. coli K-12 DNA from the Clarke and Carbon collection. The Ffm phage-sensitivity pattern (R-LPS) of the mutant was restored to the Ffm phage-resistant pattern of a smooth strain (89). Enzyme activity from the product of the cloned gene was confirmed as UDP-glucose: (heptosyl) lipopolysaccharide α-1,3-glucosyltransferase. Heterologous complementation of this Salmonella mutation is not surprising given the identical structures in this region of the core OS. The Salmonella waaG gene was subsequently cloned using a similar complementation strategy (90) and has recently been sequenced (149). Pairwise alignments of the deduced amino acid sequences of WaaG proteins from Salmonella and E. coli K-12, Rl, R2, R3, and R4 strains yield values with 85% similarity in all cases (147), correlating with the conserved glucose-α-1,3-heptose structure. A homolog of WaaG has been identified in P. aeruginosa (91,92), although its precise function is unclear since the corresponding part of the P. aeruginosa core OS has a galactosaminyl-heptose structure.
Molecular Structure and Functions of Collagen
Published in Marcel E. Nimni, Collagen, 1988
Marcel E. Nimni, Robert D. Harkness
As lysyl residues in the newly synthesized proa chains are hydroxylated, sugar residues are added to the resulting hydroxylysyl groups. Glycosylations are catalyzed by two specific enzymes, a galactosyltransferase and a glucosyltransferase.36 The first of these enzymes adds galactose to the hydroxylysyl residues, and the second adds glucose to the galactosylhydroxylsine that is formed. The galactosyltransferase from chick embryo has been purified about 1000-fold and the glucosyltransferase has been isolated as a homogeneous protein. Both enzymes are glycoproteins and their activity requires the presence of sulfhydryl groups. The activity of partially purified galactosyltransferase is separated by gel filtration into three species with apparent molecular weights of 450,000, 200,000, and 50,000 daltons. The purified glucosyltransferase has a molecular weight of 70,000 daltons. Both these transferases use sugar in a form of a uridine diphosphate glycoside, and require the presence of bivalent cations, preferably manganese.37 These enzymes, like the hydroxylases, require that the proa chains be in a nonhelical conformation. In intact cells, glycosylation is initiated while the polypeptides are still being assembled on the ribosomes, but probably continues after the release of complete proa chains in the cisternae of the rough ER; activity ceases when the chains acquire a triple-helical conformation. The oligosaccharides present in the extension peptides associated with the C-terminal region of collagen resemble those present in most other glycoproteins; they contain N-acetylglucosamine and mannose and are attached to asparagine residues.38,39 Their composition suggests that they are added as intermediates via the dolichol phosphate pathway and that final remodeling occurs in the Golgi after the helix has been formed.40 Once the translation, modifications, and additions are completed, it is essential that the individual proa chains become properly aligned for the triple helix to form. We do not know if this alignment occurs while the polypeptides are still attached to the ribosome or if they have to detach, or if the N-terminal “signal” peptide plays a role in this connection. In any case, proper alignment should juxtapose the appropriate cysteine residues as a prerequisite for formation of the disulfide bridges that link the individual proa chains at the C-terminal end. Earlier studies involving subcellular fractionation suggested that the disulfide bridges could appear during translocation of procollagen from the ribosome to the smooth endoplasmic reticulum, probably in the cisternae of the ER.41 More recently, it has been proposed that disulfide bond formation occurs while the propeptides are still attached to the ribosome.42 In any case, it seems clear that for assembly and secretion the C-terminal extensions must be present.43–45
Sabinene suppresses growth, biofilm formation, and adhesion of Streptococcus mutans by inhibiting cariogenic virulence factors
Published in Journal of Oral Microbiology, 2019
Bog-Im Park, Beom-Su Kim, Kang-Ju Kim, Yong-Ouk You
S. mutans initially attaches to the tooth surface and produces an insoluble glucan layer. The glucan is synthesized by glucosyltransferase (GTF) and contributes to the formation of polysaccharide of the dental plaque matrix, thereby accelerating the maturation of dental plaque [2,3]. S. mutans also has the ability to metabolize the carbohydrates in foods and release organic acids such as lactic acid as byproducts. The released organic acids lower the pH of the dental plaque and dissolve tooth enamel. This sucrose-dependent mechanism is also based on GTF and involves several virulence factors associated with cariogenicity, such as glucan-binding proteins (GBPs) [4].