Department of Chemistry and Biochemistry, Florida International University, Miami, Florida 33199, United States.
J Phys Chem B. 2012 Nov 1;116(43):12905-14. doi: 10.1021/jp302763h. Epub 2012 Oct 19.
Chloroperoxidase, the most versatile heme protein, has a hybrid active site pocket that shares structural features with peroxidases and cytochrome P450s. The simulation studies presented here show that the enzyme possesses a remarkable ability to efficiently utilize its hybrid structure, assuming structurally different peroxidase-like and P450-like distal pocket faces and thereby enhancing the inherent catalytic capability of the active center. We find that, during epoxidation of cis-β-methylstyrene (CBMS), the native peroxidase-like aspect of the distal pocket is diminished as the polar Glu183 side chain is displaced away from the active center and the distal pocket takes on a more hydrophobic, P450-like, aspect. The P450-like distal pocket provides a significant enthalpic stabilization of ∼4 kcal/mol of the 14 kcal/mol reaction barrier for gas-phase epoxidation of CMBS by an oxyferryl heme-thiolate species. This stabilization comes from breathing of the distal pocket. As until recently the active site of chloroperoxidase was postulated to be inflexible, these results suggest a new conceptual understanding of the enzyme's versatility: catalytic reactivity is tuned by flexibility of the distal pocket.
氯过氧化物酶是一种用途最广泛的血红素蛋白，它具有一个混合的活性位点袋，该袋与过氧化物酶和细胞色素 P450 具有结构特征。这里呈现的模拟研究表明，该酶具有出色的能力，可以有效地利用其混合结构，假设具有结构不同的过氧化物酶样和 P450 样的远端袋面，从而增强活性中心的固有催化能力。我们发现，在顺式-β-甲基苯乙烯 (CBMS) 的环氧化过程中，由于极性 Glu183 侧链从活性中心位移开，并且远端袋呈现出更疏水的 P450 样特征，因此远端袋中原有的过氧化物酶样方面会减弱。对于气相中环氧化 CBMS 的氧合铁血红素-硫醇物种，P450 样的远端袋提供了约 4 千卡/摩尔的显著焓稳定，这是反应势垒的 14 千卡/摩尔的 4 千卡/摩尔。这种稳定来自于远端袋的呼吸。由于直到最近才提出氯过氧化物酶的活性位点是不灵活的，这些结果表明了对该酶多功能性的新概念理解：通过远端袋的灵活性来调节催化反应性。
