Structure-Activity Analysis of Quorum-Sensing Signaling Peptides from Streptococcus mutans

Abstract

Streptococcus mutans secretes and utilizes a 21-amino-acid signaling peptide pheromone to initiate quorum sensing for genetic competence, biofilm formation, stress responses, and bacteriocin production. In this study, we designed and synthesized a series of truncated peptides and peptides with amino acid substitutions to investigate their structure-activity relationships based on the three-dimensional structures of S. mutans wild-type signaling peptide UA159sp and C-terminally truncated peptide TPC3 from mutant JH1005 defective in genetic competence. By analyzing these peptides, we demonstrated that the signaling peptide of S. mutans has at least two functional domains. The C-terminal structural motif consisting of a sequence of polar hydrophobic charged residues is crucial for activation of the signal transduction pathway, while the core ␣-helical structure extending from residue 5 to the end of the peptide is required for receptor binding. Peptides in which three or more residues were deleted from the C terminus did not induce genetic competence but competitively inhibited quorum sensing activated by UA159sp. Disruption of the amphipathic ␣-helix by replacing the Phe-7, Phe-11, or Phe-15 residue with a hydrophilic residue resulted in a significant reduction in or complete loss of the activity of the peptide. In contrast to the C-terminally truncated peptides, these peptides with amino acid substitutions did not compete with UA159sp to activate quorum sensing, suggesting that disruption of the hydrophobic face of the ␣-helical structure results in a peptide that is not able to bind to the receptor. This study is the first study to recognize the importance of the signaling peptide C-terminal residues in streptococcal quorum sensing.

Global transcriptional analysis of acid-inducible genes in Streptococcus mutans: multiple two-component systems involved in acid adaptation

“…3). In contrast, the cells grown at pH 7.5 had a normal transformation frequency [10 3 -10 4 transformants (mg DNA) 21 ml 21 ], similar to that reported by Li et al (2001a) and Syvitski et al (2007). Addition of CSP at neutral pH could further increase the transformation frequencies of these two strains.…”

“…One may expect the same impact when the ComCDE signal pathway is activated. This is true when CSP is added into a culture at neutral pH (Li et al, 2001a;Syvitski et al, 2007). In this case, however, the early and late competence genes were divergently regulated at low pH.…”

“…To determine the effect of acidic pH on competence development, we assayed genetic transformation of two naturally transformable strains, S. mutans UA159 and NG8, grown at pH 5.5 or 7.5 using a modified protocol (Syvitski et al, 2007). Briefly, a 1 : 20 diluted overnight culture was grown in THYE at 37 uC for 2 h. When the culture reached early to mid-exponential phase, the cell suspension was transferred into fresh pre-warmed THYE broth (1 : 10 dilution) in four test tubes, two at pH 7.5 and two at pH 5.5.…”

Regulation of d-alanylation of lipoteichoic acid in Streptococcus gordonii

“…The promoter region of the dlt operon (P dlt ; dltA GenBank ID: 157075452) was amplified by PCR using Taq DNA polymerase (New England Biolabs) and the primer pair SL624/SL625 (Table 1). The 408 bp PCR product was digested with XbaI and KpnI, and ligated into the same sites upstream of the promoterless lacZ gene carried on pSL (Syvitski et al, 2007), resulting in the creation of the plasmid pP dlt -LacZ. The plasmid confirmed by restriction analysis and PCR was maintained in E. coli XL1-blue.…”

Plausible Drug Targets in the Streptococcus mutans Quorum Sensing Pathways to Combat Dental Biofilms and Associated Risks

“…Similarly, the native CSP of Steptococcus pneumonia was known to cause chronic diseases in humans such as pneumococcal meningitis and pneumonia [13]. Earlier reports shows that the S. mutans JH1005 (deletion of three amino acid residues in the Cterminal domain of the peptide, CSP) has overexpressed bacteriocin and resulted in 600-fold reduction in the competence and drive a greater significance of those residues in QS signalling pathway [29]. The CSP has been reported to exist as a factor to be structurally random coiled and highly soluble nature to increase its diffusion rate in the aqueous environment [10,30].…”