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The HA2 haemagglutinin domain of the lysine-specific gingipain (Kgp) of Porphyromonas gingivalis promotes µ-oxo bishaem formation from monomeric iron(III) protoporphyrin IX

¹ The University of Liverpool, Oral Microbiology Group, Department of Clinical Dental Sciences, The Edwards Building, Daulby Street, Liverpool L69 3GN, UK
² Department of Microbiology, Faculty of Biotechnology, Jagiellonian University, ul. Gronostajowa 7, 30-387 Krakow, Poland
³ Department of Biochemistry and Molecular Biology, Life Science Building, University of Georgia, Athens, GA 30602, USA

Correspondence
J. W. Smalley
josmall{at}liv.ac.uk

The lysine- and arginine-specific gingipains (Kgp, and RgpA and RgpB) are the major proteinases produced by the black-pigmented periodontopathogen Porphyromonas gingivalis. They play a role in degrading host proteins, including haemoglobin, from which is formed the µ-oxo bishaem complex of iron(III) protoporphyrin IX, [Fe(III)PPIX]₂O, the major haem component of the black pigment. Kgp and RgpA bind haem and haemoglobin via the haemagglutinin-adhesin 2 (HA2) domain, but the role of this domain in the formation of µ-oxo bishaem-containing pigment is not known. UV-visible spectroscopy was used to examine the interaction of iron(III) protoporphyrin IX monomers [Fe(III)PPIX.OH] with recombinant HA2 and purified HRgpA, Kgp and RgpB gingipains. The HA2 domain reacted with Fe(III)PPIX.OH to form µ-oxo bishaem, the presence of which was confirmed by Fourier transform infrared spectroscopy. Both HRgpA and Kgp, but not RgpB, also mediated µ-oxo bishaem formation and aggregation. It is concluded that the Arg- and Lys-gingipains with HA2 haemagglutinin domains may play a crucial role in haem-pigment formation by converting Fe(III)PPIX.OH monomers into [Fe(III)PPIX]₂O and promoting their aggregation.