Porphyromonas gingivalis is a causative agent of chronic periodontitis, a disease involving progressive destruction of soft and hard tissues that support the teeth. P. gingivalis infection is also linked to increased atherosclerosis and rheumatoid arthritis. P. gingivalis lacks two enzymes in the porphyrin biosynthesis pathway and obtains porphyrins, together with the essential nutrient iron, by scavenging Fe-protoporphyrin-IX (haem) from the host. Haem uptake system component A (HusA) is essential for growth under conditions of low environmental haem. The protein can be teathered in the outer membrane of the organsism or released into the medium where it is believed to function as a haemophore, capturing haem in the environment and delivering this cargo to a cell-surface receptor. HusA is not homologous to any known haem-binding protein, suggesting that it adopts a new haem-binding fold. We are investigating the structure and porphyrin-binding function of HusA.