Characterization of the Streptococcus mutans GS-5 fruA gene encoding exo-beta-D-fructosidase

Abstract

The complete nucleotide sequence (5,010 bp) of the fructanase gene (fruA) and flanking regions of the chromosome of Streptococcus mutans GS-5 was determined. The fruA gene appears to be the sole transcript arising from a proximal promoter. The presumed precursor of the secreted FruA protein consists of 1,423 amino acids, and it has an Mr of 158,656 and a pI of 4.82. The N terminus of FruA has characteristics in common with signal peptides of gram-positive organisms. The C terminus consists of a serineand threonine-rich region, followed by the peptide LPDTGD, 4 charged amino acids, 21 amino acids with a strongly hydrophobic character, and a charged pentapeptide tail, which are proposed to correspond to the wallspanning region, the LPXTGX consensus sequence, and the membrane-spanning domains of surface-associated proteins of gram-positive cocci. The FruA protein has significant homology with the BaciUus subtilis levanase (SacC), the Bacteroidesfragilis levanase (ScrL), yeast invertases, and a number of other 1-fructosidases but not with fructosyltransferase, glucosyltransferases, or glucan-binding proteins of oral streptococci. Genes with homology to fiuA were detected in S. mutans serotype c, e, and f strains, Streptococcus ratus, Streptococcus salivarius, and Streptococcus sanguis. A deletion derivative of FruA lacking the C-terminal 437 amino acids was still functional and could hydrolyze 13-(2,6)and P-(2,1)-linked sugars, but with altered preference for substrates. The data begin to define functional domains of the FruA protein and potential regulatory sites for induction, repression, growth rate control, and posttranslational localization of this multifunctional enzyme.

Sequence Analysis of the Streptococcus mutans Ingbritt dexA Gene Encoding Extracellular Dextranase

“…2). This is consistent with the observations that most extracellular proteins from mutans streptococci appear to contain little or no cysteine (1,3,9,30,39).…”

Physical and genetic map of Streptococcus mutans GS‐5 and localization of five rRNA operons

“…All probes hybridized strongly to one fragment of each digestion pattern, with the exceptions of the fruA and the gyrB probes (Table 1A). The fruA region contains an ApaI site (8) and, consistent with this, it hybridized to both ApaI I and ApaI L/M, indicating that the ApaI I fragment is adjacent to one of the ApaI L/M fragments on the physical map. The gyrB probe was obtained by PCR from S. mutans GS-5 DNA using degenerate primers (45).…”

A novel signal transduction system and feedback loop regulate fructan hydrolase gene expression in Streptococcus mutans

“…Together with the real-time PCR results, these data demonstrate that the LevQRST pathway is required for the induction of EII Lev by fructose. At first, these results may seem contradictory, because, as we have described, expression of fruA in S. mutans is dramatically higher when the cells are grown in inulin or levans, than when fructose is the growth substrate (Jacques et al, 1985;Burne and Penders, 1992;Burne et al, 1999;Wen and Burne, 2002). One interpretation is that the LevQRST system binds fructose or fructose-containing polymers to mediate induction of its targets.…”