Novel structural properties of a haemophore-like protein offer an avenue for targeted elimination of Porphyromonas gingivalis

Kwan A1, Gao J2, Yammine A1, Zhou Z2, Nguyen K2, Hunter N2 and Gell D3

  1. School of Life and Environmental Sciences, University of Sydney, NSW 2006, Australia.
  2. Institute of Dental Research, Westmead Hospital, University of Sydney, NSW 2145, Australia.
  3. School of Medicine, University of Tasmania, TAS 7005, Australia.

Porphyromonas gingivalis is a keystone bacterium found in chronic periodontal disease, which is characterised by severe inflammation and destruction of supportive tooth structures. The disease has also been linked to systemic pathologies including cardiovascular diseases and autoimmune disorders1. P. gingivalis growth is dependent on the acquisition of environmental haem for its iron and porphyrin requirements. As such, the bacterium has an array of proteins for haem acquisition, including HusA (Heme uptake system protein A). In previous work2, we have shown that HusA directly binds haem and is essential for P. gingivalisto grow under haem-limiting conditions, such as those found inside plaques and in saliva. Therefore, HusA may represent a therapeutic target for treating chronic periodontitis and possibly other associated systemic diseases. To develop compounds that target HusA and P. gingivalis, we have determined the solution structure of HusA using Nuclear Magnetic Resonance (NMR) spectroscopy. Using NMR titration studies, mutagenesis and in silico docking, we have identified that haem binds in a hydrophobic groove on the α-helical structure that lacks the typical iron coordination seen in other haemophores. This mode of interaction allows HusA to bind a variety of abiotic and metal-free porphyrins with significantly higher affinity than to haem. We have exploited the unusual porphyrin binding activity of HusA to target a prototypical deuteroporphyrin-metronidazole conjugate with restricted antimicrobial specificity in a “Trojan horse” strategy that effectively kills intracellular P. gingivalis. Therefore, targeting and manipulating HusA:porphyrin interactions is a promising avenue to developing new therapeutics against P. gingivalis. 1. Seymour GJ, Ford PJ, Cullinan MP, Leishman S, Yamazaki K. (2007) Relationship between periodontal infections and systemic disease. Clin Microbiol Infec 13:3. 2. Gao JL, Nguyen KA, Hunter NJ. (2010) Characterization of a hemophore-like protein from Porphyromonas gingivalis. J Biol Chem 285:40028. .