O'Maille Paul E, Malone Arthur, Dellas Nikki, Andes Hess B, Smentek Lidia, Sheehan Iseult, Greenhagen Bryan T, Chappell Joe, Manning Gerard, Noel Joseph P
Howard Hughes Medical Institute, The Salk Institute for Biological Studies, Jack H. Skirball Center for Chemical Biology & Proteomics, 10010 North Torrey Pines Road, La Jolla, California 92037, USA.
Nat Chem Biol. 2008 Oct;4(10):617-23. doi: 10.1038/nchembio.113. Epub 2008 Sep 7.
Throughout molecular evolution, organisms create assorted chemicals in response to varying ecological niches. Catalytic landscapes underlie metabolic evolution, wherein mutational steps alter the biosynthetic properties of enzymes. Here we report the first systematic quantitative characterization of the catalytic landscape underlying the evolution of sesquiterpene chemical diversity. On the basis of our previous discovery of a set of nine naturally occurring amino acid substitutions that functionally interconverted orthologous sesquiterpene synthases from Nicotiana tabacum and Hyoscyamus muticus, we created a library of all possible residue combinations (2(9) = 512) in the N. tabacum enzyme. The product spectra of 418 active enzymes revealed a rugged landscape where several minimal combinations of the nine mutations encode convergent solutions to the interconversions of parental activities. Quantitative comparisons indicated context dependence for mutational effects--epistasis--in product specificity and promiscuity. These results provide a measure of the mutational accessibility of phenotypic variability in a diverging lineage of terpene synthases.
在整个分子进化过程中，生物体针对不同的生态位产生各种各样的化学物质。催化景观是代谢进化的基础，其中突变步骤会改变酶的生物合成特性。在此，我们报告了对倍半萜化学多样性进化背后催化景观的首次系统定量表征。基于我们之前的发现，即一组九个天然存在的氨基酸替换可在功能上相互转换烟草（Nicotiana tabacum）和天仙子（Hyoscyamus muticus）直系同源倍半萜合酶，我们构建了烟草酶中所有可能残基组合（2⁹ = 512）的文库。418种活性酶的产物谱揭示了一个崎岖的景观，其中九个突变的几个最小组合编码了亲本活性相互转换的趋同解决方案。定量比较表明，在产物特异性和混杂性方面，突变效应存在背景依赖性——上位性。这些结果提供了一种衡量萜类合酶分化谱系中表型变异突变可及性的方法。
