Sharma Vivek, Wikström Mårten, Kaila Ville R I
Helsinki Bioenergetics Group, Structural Biology and Biophysics Programme, Institute of Biotechnology, PB 65 (Viikinkaari 1), University of Helsinki, FIN 00014, Helsinki, Finland.
Biochim Biophys Acta. 2010 Aug;1797(8):1512-20. doi: 10.1016/j.bbabio.2010.03.004. Epub 2010 Mar 7.
Cytochrome cbb3 is a distinct member of the superfamily of respiratory heme-copper oxidases, and is responsible for driving the respiratory chain in many pathogenic bacteria. Like the canonical heme-copper oxidases, cytochrome cbb3 reduces oxygen to water and couples the released energy to pump protons across the bacterial membrane. Homology modeling and recent electron paramagnetic resonance (EPR) studies on wild type and a mutant cbb3 enzyme [V. Rauhamäki et al. J. Biol. Chem. 284 (2009) 11301-11308] have led us to perform high-level quantum chemical calculations on the active site. These calculations bring molecular insight into the unique hydrogen bonding between the proximal histidine ligand of heme b3 and a conserved glutamate, and indicate that the catalytic mechanism involves redox-coupled proton transfer between these residues. The calculated spin densities give insight in the difference in EPR spectra for the wild type and a recently studied E383Q-mutant cbb3-enzyme. Furthermore, we show that the redox-coupled proton movement in the proximal cavity of cbb3-enzymes contributes to the low redox potential of heme b3, and suggest its potential implications for the high apparent oxygen affinity of these enzymes.
细胞色素cbb3是呼吸血红素-铜氧化酶超家族中的一个独特成员，负责驱动许多致病细菌中的呼吸链。与典型的血红素-铜氧化酶一样，细胞色素cbb3将氧气还原为水，并将释放的能量与跨细菌膜泵送质子相偶联。对野生型和突变型cbb3酶的同源建模以及最近的电子顺磁共振（EPR）研究[V. Rauhamäki等人，《生物化学杂志》284 (2009) 11301 - 11308]促使我们对活性位点进行高水平的量子化学计算。这些计算使我们对血红素b3的近端组氨酸配体与保守谷氨酸之间独特的氢键有了分子层面的认识，并表明催化机制涉及这些残基之间的氧化还原偶联质子转移。计算得到的自旋密度揭示了野生型和最近研究的E383Q突变型cbb3酶的EPR光谱差异。此外，我们表明cbb3酶近端腔中的氧化还原偶联质子运动导致了血红素b3的低氧化还原电位，并提出了其对这些酶的高表观氧亲和力的潜在影响。
