Mao W, Schuler M A, Berenbaum M R
Department of Entomology, University of Illinoism Urbana, IL, USA.
Insect Mol Biol. 2007 Aug;16(4):481-90. doi: 10.1111/j.1365-2583.2007.00741.x.
Although substrate-specific CYP6B1 and CYP6B3 enzymes in Papilio polyxenes contribute to specialization on furanocoumarin-containing host plants, CYP6B4 and CYP6B17 enzymes in the polyphagous Papilio glaucus and Papilio canadensis have a broader range of substrates. Papilio multicaudatus, an oligophage with one furanocoumarin-containing host, is putatively ancestral to polyphagous Papilio species. Furanocoumarin-inducible CYP6B33-CYP6B37 and CYP6AB6 were characterized from this species. Heterologous expression of CYP6B33 revealed furanocoumarin metabolism resembling that of CYP6B4-CYP6B17 enzymes from P. glaucus and P. canadensis. Molecular models of CYP6B33 and CYP6B4 indicate that seven conserved aromatic side chains stabilize their hydrophobic catalytic sites and that a Lys484-Ser484 substitution enlarges the CYP6B4 active site pocket to increase the predicted distance between the substrate and reactive oxygen relative to CYP6B1. Loss of specialization in this lineage may have resulted from relatively few mutational changes, allowing acquisition of broader catalytic activities without loss of ancestral furanocoumarin-metabolizing activities.
虽然金凤蝶中底物特异性的CYP6B1和CYP6B3酶有助于其适应含呋喃香豆素的寄主植物，但多食性的北美大黄凤蝶和加拿大凤蝶中的CYP6B4和CYP6B17酶具有更广泛的底物范围。多尾凤蝶是一种寡食性昆虫，其寄主植物中含有一种呋喃香豆素，推测它是多食性凤蝶物种的祖先。从该物种中鉴定出了呋喃香豆素诱导型的CYP6B33 - CYP6B37和CYP6AB6。CYP6B33的异源表达显示其呋喃香豆素代谢与北美大黄凤蝶和加拿大凤蝶的CYP6B4 - CYP6B17酶相似。CYP6B33和CYP6B4的分子模型表明，七个保守的芳香族侧链稳定了它们的疏水催化位点，并且赖氨酸484 - 丝氨酸484的取代扩大了CYP6B4的活性位点口袋，相对于CYP6B1增加了底物与活性氧之间的预测距离。该谱系中专业化的丧失可能是由于相对较少的突变变化导致的，使得在不丧失祖先呋喃香豆素代谢活性的情况下获得了更广泛的催化活性。
