RT Journal Article SR Electronic T1 Structural basis of the Cope rearrangement and C–C bond-forming cascade in hapalindole/fischerindole biogenesis JF bioRxiv FD Cold Spring Harbor Laboratory SP 173674 DO 10.1101/173674 A1 Sean A. Newmister A1 Shasha Li A1 Marc Garcia-Borràs A1 Jacob N. Sanders A1 Song Yang A1 Andrew N. Lowell A1 Fengan Yu A1 Janet L. Smith A1 Robert M. Williams A1 K. N. Houk A1 David H. Sherman YR 2017 UL http://biorxiv.org/content/early/2017/08/08/173674.abstract AB STRUCTURES The atomic coordinates and structure factors for:HpiC1 W73M/K132M SeMet (P212121) –1.7 ÅHpiC1 native (C2) –1.5 ÅHpiC1 native (P42) –2.1 ÅHpiC1 Y101F (C2) –1.4 ÅHpiC1 Y101S (C2) –1.4 ÅHpiC1 F138S (P21) –1.7 ÅHpiC1 Y101F/F138S (P21 –1.65 Å have been deposited with the Research Collaboratory for Structural Bioinformatics as Protein Data Bank entries 5WPP, 5WPR, 6AL6, 5WPR, 5WPU, 6AL7, and 6AL8 (www.rcsb.org).GRANTS This work was supported by: The authors thank the National Science Foundation under the CCI Center for Selective C-H Functionalization (CHE-1205646), the National Institutes of Health (CA70375 to RMW and DHS), R35 GM118101, R01 GM076477 and the Hans W. Vahlteich Professorship (to DHS) for financial support. M.G-B. thanks the Ramón Areces Foundation for a postdoctoral fellowship. J.N.S. acknowledges the support of the National Institute of General Medical Sciences of the National Institutes of Health under Award Number F32GM122218. Computational resources were provided by the UCLA Institute for Digital Research and Education (IDRE) and the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by the NSF (OCI-1053575). The content does not necessarily represent the official views of the National Institutes of Health.ABSTRACT Hapalindole alkaloids are a structurally diverse class of cyanobacterial natural products defined by their varied polycyclic ring systems and diverse biological activities. These polycyclic scaffolds are generated from a common biosynthetic intermediate by the Stig cyclases in three mechanistic steps, including a rare Cope-rearrangement, 6-exo-trig cyclization, and electrophilic aromatic substitution. Here we report the structure of HpiC1, a Stig cyclase that catalyzes the formation of 12-epi-hapalindole U in vitro. The 1.5 Å structure reveals a dimeric assembly with two calcium ions per monomer and the active sites located at the distal ends of the protein dimer. Mutational analysis and computational methods uncovered key residues for an acid catalyzed [3,3]-sigmatropic rearrangement and specific determinants that control the position of terminal electrophilic aromatic substitution leading to a switch from hapalindole to fischerindole alkaloids.