Production and properties of adhesin-free gingipain proteinase RgpA

The Arg-specific gingipains of Porphyromonas gingivalis RgpA and RgpB have 97% identical sequences in their catalytic domains yet their propeptides are only 76% identical. RgpA isolates as a proteinase–adhesin complex (HRgpA) which hinders direct kinetic comparison of RgpA cat as a monomer with monomeric RgpB. We tested modifications of rgpA identifying a variant that enabled us to isolate histidine-tagged monomeric RgpA (rRgpAH). Kinetic comparisons between rRgpAH and RgpB used benzoyl- l -Arg-4-nitroanilide with and without cysteine and glycylglycine acceptor molecules. With no glycylglycine, values of K m , V max , k cat and k cat / K m for each enzyme were similar, but with glycylglycine K m decreased, V max increased and k cat increased ~ twofold for RgpB but ~ sixfold for rRgpAH. The k cat / K m for rRgpAH was unchanged whereas that of RgpB more than halved. Recombinant RgpA propeptide inhibited rRgpAH and RgpB with K i 13 nM and 15 nM K i respectively slightly more effectively than RgpB propeptide which inhibited rRgpAH and RgpB with K i 22 nM and 29 nM respectively ( p