Pathway for Uptake and Degradation of X-Prolyl Tripeptides in Streptococcus mutans VA-29R and Streptococcus sanguis ATCC 10556

Abstract

The growth of Streptococcus mutans and Streptococcus sanguis in the oral environment requires that these micro-organisms be able to degrade salivary proteins and to assimilate the resulting peptides as an amino nitrogen source. Our research is aimed at the definition of the proteolytic enzyme systems in these oral streptococci which allow them to utilize such substrates. In the present work, the nature of the hydrolytic activity expressed by S. mutans VA-29R and S. sanguis ATCC 10556 against X-Pro4-nitroanilide and X-Pro-Y tripeptide substrates was investigated. This activity was predominantly associated with a cytoplasmic dipeptidyl peptidase which preferentially catalyzes the release of an N-terminal dipeptide from substrates in which proline is the penultimate residue. These streptococci also possess a second cytoplasmic peptidase, pepD, which catalyzes the hydrolysis of X-Pro dipeptides. We found that Gly-Pro-Ala or Ala-Pro-Gly were transported into the bacterial cells only when an energy source such as glucose was present. Peptide uptake was time-dependent, and selective exodus of peptide-derived amino acids from the bacterial cells occurred during peptide uptake. Results from these studies provide evidence that S. mutans VA-29R and S. sanguis ATCC 10556 possess a pathway for the complete degradation of X-Pro tripeptides. Transport of the peptides into cells prior to hydrolysis provides an efficient way by which all amino acids of a peptide may be obtained at an energy expense equivalent to that associated with the transport of just one amino acid. In light of the abundance of proline in salivary polypeptides, this degradative pathway could be an important component in the proteolytic pathway for salivary polypeptide utilization in these oral streptococci.

Novel Extracellular x-Prolyl Dipeptidyl-Peptidase (DPP) from Streptococcus gordonii FSS2: an Emerging Subfamily of Viridans Streptococcal x-Prolyl DPPs

“…This activity has been described in studies concerning tripeptide degradation systems of S. sanguinis and S. mutans (8) and collagen degradation by S. gordonii Challis in the IE model (19). Our work presents the first biochemical and genetic studies of purified enzyme.…”

“…A tripeptide transport system was identified in S. sanguinis that permitted the assimilation of free amino acids by membrane-bound and intracellular proteolysis. It was further concluded that x-prolyl dipeptides were insufficient for transport (8). This is counterintuitive to the action of Sg-xPDPP that results in high concentrations of extracellular dipeptides.…”

“…Certainly, proteolytic and peptide transport systems for viridans members have been described (1,7,17,18,25,45,54), and it has been shown that small peptides can be imported into S. sanguinis, while those exceeding size limitations would require further hydrolysis by endo-and exopeptidases present on the surface or secreted by these cells (8). One such activity that facilitates these metabolic requirements, a dipeptidyl peptidase (DPP) with Gly-Pro-pNa hydrolyzing activity, has been detected in culture supernatant of S. gordonii (8,19) yet has remained undefined. In this report we describe the purification, characterization, and cloning of a novel extracellular x-prolyl DPP that derives from S. gordonii FSS2 (Sg-xPDPP), a strain previously isolated from the bloodstream of a patient with subacute bacterial endocarditis (SBE).…”

Proteolytic degradation of human salivary MUC5B by dental biofilms

“…Streptococcus mutans and Streptococcus sanguinis also contain complex proteolytic pathways necessary for growth (e.g. Cowman & Baron, 1997). In contrast, supragingival plaque from macaque monkeys expresses both exoglycosidases and a wide range of proteolytic activities (Smith & Beighton, 1986.…”

Extracellular Arginine Aminopeptidase from Streptococcus gordonii FSS2

“…The utilization of the amino acid is then prioritized, so the transport and metabolism of arginine-containing peptides may become particularly important. The amino acid and peptide transport systems of viridans streptococci have been described previously (2,5,10,25,31), and it has been shown that amino acids and small peptides are readily imported while those exceeding size limitations require hydrolysis by endo-and exopeptidases either present on the surface or secreted by these cells (6). One such activity that could meet the transport and metabolic challenges in vivo is an arginine aminopeptidase.…”