Structural and functional insights into the iminium ion intermediate in AsKslB-mediated Pictet-Spengler reaction
Year: 2025
Type: article
Abstract: Pictet–Spengler (PS) reactions are pivotal in the biosynthesis of bioactive alkaloids and pharmaceuticals, yet key structural details underlying their enzymatic catalysis remain insufficiently understood. We identified AsKslB from Actinosynnema sp. ALI-1.44 as a Pictet-Spenglerase with broad substrate scope that catalyzes the stereoselective condensation of l -tryptophan ( l -Trp) and α-ketoglutarate (α-KG) to form kitasetalic acid (KA), a tetrahydro-β-carboline (THβC). High-resolution crystal structures of apo, substrate-, intermediate-, and product-bound forms elucidate the full catalytic trajectory and key residues. Crucially, the elusive iminium ion intermediate (IM-1) and a synchronously released water molecule are captured, providing direct structural evidence for the initiating cyclization step of Pictet-Spengler reaction. Glu276 undergoes conformational changes essential for catalysis. These findings offer detailed mechanistic insights into Pictet-Spenglerase function and establish AsKslB as a promising biocatalyst for stereoselective N -heterocycle synthesis.
Authors: Yan-Bin Teng, Zhi Qiao, Chunya Xie, Xiaona Yang, Xinyu Liu, Zhengrong Zou, Yunchang Xie, Xuan Zhang, Qi Chen
Language: English
Subfield: Pharmacology
Field: Medicine
Domain: Health Sciences
Open Access status: gold
Estimated APC paid: $1,500
Funders: National Natural Science Foundation of China, Anhui Medical University, Natural Science Foundation of Jiangxi Province, Anhui Provincial Department of Science and Technology, Scientific Research Foundation of Education Department of Anhui Province of China, Natural Science Foundation of Anhui Province, University Natural Science Research Project of Anhui Province
OpenAlex ID: W4414517471