Bait Region Cleavage and Complex Formation ofHuman I-2M with a Porphyromonas gingivalisW50 ProteaseIs Not Accompanied by Enzyme Inhibition

Three isoforms of extracellular Arg-specific proteases of P. gingivalis, W50, HRgpA, RgpAcat and mt-RgpAcat, which are all products of the same gene, show identical enzymatic properties toward small chromogenic substrates but have different subunit organisation and molecular size. In order to examine the potential inhibition of these proteases in vivo by host protease inhibitors, the interaction of HRgpA (~ 110 kDa) and RgpAcat (~ 55 kDa) with human I-2M and their cytotoxicity toward cultured fibroblasts were investigated. Both enzymes formed complexes with I-2M as shown by gel filtration chromatography and both cleaved the abaita region at Arg-Leu. However, whereas (I-2M-RgpAcat) complex was unable to hydrolyse large substrates such as hide powder azure, (I-2M-HRgpA) complex hydrolysed both small and large substrates. HRgpA was able to bind to I-2M saturated with trypsin and also to methylamine-treated I-2M. This suggested that HRgpA is able to bind to both aslowa and afasta forms of I-2M and formation of (I-2M:HRgpA) complex does not trap HRgpA and cause inhibition of activity toward hide powder azure. However, the (I-2M-HRgpA) complex is not able to cleave other I-2M molecules, which suggests that the active site of HRgpA in the complex is constrained probably due to steric reasons. The (I-2M-HRgpA) complex was cytotoxic to 3T3 cells, causing them to round up and detach from the surface with a reduction in metabolic activity.