A 46-kDa hemolytic protein, referred to as cystalysin, from Treponema denticola ATCC 35404 was overexpressed in Escherichia coli LC-67. Both the native and recombinant 46-kDa proteins were purified to homogeneity. Both proteins expressed identical biological and functional characteristics. In addition to its biological function of lysing erythrocytes and hemoxidizing the hemoglobin to methemoglobin, cystalsin was also capable of removing the sulfhydryl and amino groups from selected S-containing compound (e.g., cysteine) producing H2S, NH3, and pyruvate. This cysteine desulfhydrase resulted in the following Michaelis-Menten kinetics: K(m) = 3.6 mM and k(cat) = 12 s-1. Cystathionine and S-aminoethyl-L-cysteine were also substrates for the protein. Gas chromatography-mass spectrometry and high-performance liquid chromatography analysis of the end products revealed NH3, pyruvate, homocysteine (from cystathionine), and cysteamine (from S-aminoethyl-L- cysteine). The enzyme was active over a broad pH range, with highest activity at pH 7.8 to 8.0. The enzymatic activity was increased by β-mercaptoethanol. It was not inhibited by the proteinase inhibitor TLCK (Nα-p-tosyl-L-lysine chloromethyl ketone), pronase, or proteinase K, suggesting that 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 activity of an αC-N and βC-S lyase (cystathionase) type. Since large amounts of H2S have been reported in deep periodontal pockets, cystalysin may also function in vivo as an important virulence molecule.
ASJC Scopus subject areas
- Infectious Diseases