Structural basis for stereoselective dehydration and hydrogen-bonding catalysis by the SAM-dependent pericyclase LepI
作者单位：State Key Laboratory of Bio-organic and Natural Products ChemistryCenter for Excellence in Molecular SynthesisShanghai Institute of Organic ChemistryCAS Department of Chemistry and BiochemistryDepartment of Chemical and Biomolecular EngineeringUniversity of California Los Angeles
会议名称：《第十一届全国化学生物学学术会议》
会议日期：2019年
学科分类：081705[工学-工业催化] 08[工学] 0817[工学-化学工程与技术]
关 键 词：pericyclase crystal structure SAM
摘 要：LepI is an S-adenosylmethionine（SAM）-dependent pericyclase that catalyses the formation of 2-pyridone natural product leporin C. Biochemical characterization has shown that LepI can catalyse stereoselective dehydration to yield a reactive（E）-quinone methide that can undergo bifurcating intramolecular Diels–Alder（IMDA） and hetero-Diels–Alder（HDA） cyclizations from an ambimodal transition state, as well as a [3,3]-retro-Claisen rearrangement to recycle the IMDA product into leporin C. Here, we solve the X-ray crystal structures of SAM-bound LepI and in complex with a substrate analogue（the product leporin C） and a retro-Claisen reaction transition-state analogue to understand the structural basis for the multitude of reactions. Structural and mutational analysis reveals how nature evolves a classic methyltransferase active site into one that can serve as a dehydratase and a multifunctional pericyclase. Catalysis of both sets of reactions employs H133 and R295, two activesite residues that are not found in canonical methyltransferases. An alternative role of SAM, which is not found to be in direct contact with the substrate, is also proposed.