Cystalysin, a 46-kDa L-cysteine desulfhydrase from Treponema denticola: Biochemical and biophysical characterization

A 46-kDa hemolytic protein referred to as cystalysin, from Treponema denticola ATCC 35404, was characterized and overexpressed in Escherichia coli LC-67. Cystalysin lysed erythrocytes, hemoxidized hemoglobin to sulfhemoglobin and methemoglobin, and removed the sulfhydryl and amino group from selected S-containing compounds (e.g., cysteine) producing H₂S, NH₃, and pyruvate. With L-cysteine as substrate, cystalysin obeys Michaelis- Menten kinetics. Cystathionine and s-aminoethyl-L-cysteine were also substrates. Several of the small alpha amino acids were found to be competitive inhibitors of cystalysin. The enzymatic activity was increased by β-mercaptoethanol and was not inhibited by the proteinase inhibitor TLCK (Nα-p-tosyl-L-lysine chloromethyl ketone), pronase, or proteinase K, suggesting the functional site was physically protected or located in a small fragment of the polypeptide. We hypothesize that cystalysin is a pyridoxal- 5-phosphate-containing enzyme with the activity of an αC-N and βC-S lyase (cystathionase). Since high amounts of H₂S have been reported in deep periodontal pockets, this metabolic enzyme from T. denticola may also function in vivo as an important virulence molecule.