Dehaloperoxidase from Amphitrite Ornata: Structures of the Native and Substrate-Complexed Enzyme. Lukasz Lebioda¹, Michael W. LaCount¹, Erli Zhang², Yung-Pin Chen³, ¹Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, USA, ²Parke-Davis, Ann Arbor, MI, ³Department of Biology, University of South Carolina, Columbia, SC 29208, USA

The terebellid polychaete Amphitrite ornata produces high levels of a unique dehalogenating peroxidase (DHP) capable of converting halogenated phenols into halogenated quinones. Native DHP is a heme protoporphyrin IX-containing enzyme consisting of two identical subunits (M_r = 15,529). X-ray diffraction data sets have been collected to 1.8 Å (native) and 2.0 Å (iodophenol derivative) resolution. Crystals are orthorhombic space group P2₁2₁2₁ with unit cell dimensions a = 68.5 Å, b = 68.4 Å and c = 61.0 Å. Multiple isomorphous replacement with Hg²⁺ and 4-iodophenol derivatives and anomalous scattering signal from the native protein were used to calculate the initial phases for DHP. The current model has been refined to R = 25 % without solvent molecules. The protein fold is very similar to the globin fold and this similarity indicates that DHP evolved from a common ancestral gene most likely encoding for an oxygen carrier. A derivative data set collected on a DHP-4-iodophenol complex yielded the first structure of a peroxidase-organic substrate complex. We have identified the position of the iodine atom on the basis of positive F_o - F_c density above 4[sigma]. These structural analyses of DHP should be able to provide insights into how the function of DHP arose on the molecular scafolding of typical globins, such as myoglobin.