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 dentic ola 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 selecte d S-containing compounds (e.g,, cysteine) producing H2S, NH3 and pyruvate. With L-cysteine as substrate, cystalysin obeys Michaelis-Menten kinetics. C ystathionine and s-aminoethyl-L-cysteine were also substrates. Several of t he small alpha amino acids were found to be competitive inhibitors of cysta lysin. The enzymatic activity was increased by beta-mercaptoethanol and was not inhibited by the proteinase inhibitor TLCK (N alpha-p-tosyl-L-lysine c hloromethyl ketone), pronase, or proteinase K, suggesting the functional si te was physically protected or located in a small fragment of the polypepti de. We hypothesize that cystalysin is a pyridoxal-5-phosphate-containing en zyme with the activity of an alpha C-N and PC-S lyase (cystathionase). Sinc e high amounts of H2S have been reported in deep periodontal pockets, this metabolic enzyme from T. denticola may also function in vivo as an importan t virulence molecule.