HTHP is from the marine bacterium Silicibacter pomeroyi and has peroxidase and catalase activity. HTHP consists of six monomers which each binds a solvent accessible heme group and is stabilised by the interaction of three neighbouring monomers [1]. The heme iron is penta-coordinated with a tyrosine residue as proximal ligand [1].

1: HTHP: a novel class of hexameric, tyrosine-coordinated heme proteins. Jeoung JH, Pippig DA, Martins BM, Wagener N, Dobbek H; J Mol Biol. 2007;368:1122-1131. PMID:17395199