Cell surface proteases are a major virulence factor of many pathogenic bacteria. Porphyromonas gingivalis is the keystone pathogen associated with chronic periodontitis. The bacterium’s main virulence factors are the cell surface-located cysteine proteases, the Arg-gingipains (RgpA, RgpB) and the Lys-gingipain (Kgp). All three gene products contain a signal peptide of ~22 amino acids in length, a propeptide of around 200 amino acids in length, and a catalytic domain ~480 amino acids long. In addition, rgpA and kgp encode haemagglutinin-adhesin domains in the polypeptide region C-terminal to the catalytic domain. Furthermore, there are several domains of unknown function flanking the catalytic or adhesin domains. One such domain contains sequence motifs previously proposed to be responsible for the ability of the catalytic domain to bind the cell surface through its flanking adhesins. The aim of this study is to characterise these domains to elucidate their role in catalysis. The recombinant form of the 100 residue adhesin-flanking domain (designated ABM1,2,3) of unknown function was produced in E. coli. The solubility, chromatographic, and electrophoretic behaviour were examined. This domain demonstrated high solubility with a high propensity to form stable oligomers. The minimum oligomer consisted of three subunits. In conclusion, the recombinant form of this adhesin-flanking domain (ABM1,2,3) displays a conformational preference and forms stable oligomers in vitro.