2OYY

HTHP: a hexameric tyrosine-coordinated heme protein

Summary for 2OYY

• Entry DOI: 10.2210/pdb2oyy/pdb
• Descriptor: Hexameric cytochrome, IODIDE ION, PROTOPORPHYRIN IX CONTAINING FE (3 entities in total)
• Functional Keywords: all helical, unknown function
• Biological source: Silicibacter pomeroyi
• Total number of polymer chains: 8
• Total formula weight: 73418.57

Authors

Dobbek, H. (deposition date: 2007-02-23, release date: 2007-04-10, Last modification date: 2024-02-21)

Primary citation

Jeoung, J.H.,Pippig, D.A.,Martins, B.M.,Wagener, N.,Dobbek, H.
HTHP: A Novel Class of Hexameric, Tyrosine-coordinated Heme Proteins
J.Mol.Biol., 368:1122-1131, 2007

PubMed Abstract: We have cloned, expressed, isolated and characterized a hexameric tyrosine-coordinated heme protein (HTHP) from the marine bacterium Silicibacter pomeroyi. HTHP shows peroxidase and catalase activity and has a high thermal stability. As-isolated HTHP has absorption maxima at 407, 495, 504, 532 and 622 nm wavelength. Upon reduction maxima at 430, 564 and 596 nm wavelength are discernible. The crystal structure of HTHP reveals a hexameric, ring-like arrangement of six monomers. Each monomer binds a solvent accessible heme group, which is stabilized by the interaction of three neighboring monomers. The pocket around the heme distal side is positively charged due to three conserved arginine residues in direct vicinity. The heme iron is penta-coordinated with a tyrosine residue as proximal ligand. The coordinating hydroxyl-group of the tyrosine ligand interacts with the guanidinium group of a nearby arginine residue, an arrangement closely resembling the catalytic dyad found in monofunctional heme-containing catalases and coral allene oxide synthases, which are b-type cytochromes with tyrosine coordination trans to an empty coordination site. Despite the similarity in heme coordination HTHP is functionally and structurally unrelated to catalases and other heme-containing proteins. Its hexameric arrangement, solvent accessible heme binding pocket and heme coordination by tyrosine render HTHP a unique protein with unusual properties. A database search against complete and incomplete genomes shows that the 76 amino acid residues sequence of HTHP is unrelated to characterized proteins, but is homologous to orfs found in a phylogenetically diverse set of bacteria with sequence identities of 30-76%. We therefore propose that HTHP is the prototype of a new class of heme proteins.

PubMed: 17395199
DOI: 10.1016/j.jmb.2007.02.079

Experimental method

X-RAY DIFFRACTION (2.5 Å)