Porphyromonas gingivalis is a major pathogen in chronic periodontitis. A major virulence factor of P. gingivalis is the extracellular non-covalently associated complexes of Arg-X- and Lys-X-specific cysteine proteinases and adhesins designated the RgpA-Kgp complexes. We hypothesized that a sequence motif designated adhesin-binding motif 1 (ABM1) present within C-terminal segment of the catalytic domains and repeated in the adhesin domains, is responsible for the non-covalent association of these domains into the complexes. Objectives: The aim of this study was to investigate the hypothesis that ABM1 is the binding motif that non-covalently attaches Kgpcat to the adhesins of the RgpA-Kgp complexes. Methods: A series of recombinant mutant strains were constructed to facilitate the deletion of nucleotides encoding the Kgpcat ABM1 from kgp in P. gingivalis W50 using DNA-SOEing and allele-exchange. The ABM1- strain was assessed for Lys-Xaa and Arg-Xaa cleavage activity at exponential phase and after 3 and 6 days of incubation. Results: Surface-associated Lys-Xaa proteolytic activity of whole cells of the ABM1- strain was abolished however low levels of Lys-X activity were observed in the culture supernatant during exponential growth that increased markedly (x12) by 3 days incubation. Arg-Xaa activity was not affected. SDS-PAGE combined with mass spectrometry revealed that during exponential growth there was an accumulation of 74 kDa and 64 kDa proteins in the mutant culture fluid that were Kgpcat with a complete and partial prodomain respectively. After 3 days of incubation abundant, mature, 48 kDa Kgpcat enzyme was observed. Conclusions: In the absence of ABM1, Kgpcat was unable to incorporate into the RgpA-Kgp complex and was released from the cell surface in a precursor form that was subsequently processed. This result supports the hypothesis that ABM1 is an intra-complex binding motif.