Identification of lysine decarboxylase as a mammalian cell growth inhibitor in Eikenella corrodens: possible role in periodontal disease

The pathogenesis of inflammatory periodontal disease was studied by examini ng the mechanism of HeLa and HL60 cell growth inhibition by cell-free salin e-soluble extracts of Eikenella corrodens and bacterial plaque. Previous st udies identified a protein (p80) as causing growth inhibition by E. corrode ns extracts. After purification by two-dimensional SDS-PAGE, p80 was digest ed with protease lysC. Amino acid sequences were obtained and backtranslate d for use as PCR primers. A 5840 nucleotide sequence containing a lysine de carboxylase gene was obtained from a Sau3A1 genomic library of E. corrodens DNA. Lysine decarboxylase activity was present at physiologic pH in the E. corrodens extracts containing p80, and also in bacterial plaque. Both extr acts caused growth inhibition by depleting lysine from cell culture media t hrough conversion to cadaverine. Adding lysine, or immune goat IgG to a pep tide derived from the active site sequence of E. corrodens lysine decarboxy lase, retarded lysine depletion and growth inhibition. E-Amino caproic acid specifically enhanced lysine decarboxylase activity at the low lysine conc entration in HL60 cell culture media, and also increased the growth inhibit ion. Thus, lysine decarboxylases such as p80 inhibit growth by removing lys ine from mammalian cell culture media. A new role for lysine decarboxylase activity in the microbial aetiology of periodontal disease is discussed. (C ) 2001 Academic Press.