CRYSTAL-STRUCTURE OF CATALASE HPII FROM ESCHERICHIA-COLI

Background: Catalase is a ubiquitous enzyme present in both the prokar yotic and eukaryotic cells of aerobic organisms. It serves, in part, t o protect the cell from the toxic effects of small peroxides. Escheric hia coli produces two catalases, HPI and HPII, that are quite distinct from other catalases in physical structure and catalytic properties. HPII, studied in this work, is encoded by the katE gene, and has been characterized as an oligomeric, monofunctional catalase containing one cis-heme d prosthetic group per subunit of 753 residues. Results: The crystal structure of catalase HPII from E. coli has been determined t o 2.8 Angstrom resolution. The asymmetric unit of the crystal contains a whole molecule, which is a tetramer with accurate 222 point group s ymmetry. In the model built, that includes residues 27-753 and one hem e group per monomer, strict non-crystallographic symmetry has been mai ntained. The crystallographic agreement R-factor is 20.1% for 58477 re flections in the resolution shell 8.0-2.8 Angstrom. Conclusions: Despi te differences in size and chemical properties, which were suggestive of a unique catalase, the deduced structure of HPII is related to the structure of catalase from Penicillium vitale, whose sequence is not y et known. In particular, both molecules have an additional C-terminal domain that is absent in the bovine catalase. This extra domain contai ns a Rossmann fold but no bound nucleotides have been detected, and it s physiological role is unknown. In HPII, the heme group is modified t o a heme d and inverted with respect to the orientation determined in all previously reported heme catalases. HPII is the largest catalase f or which the structure has been determined to almost atomic resolution .