An Unusual Ferryl Intermediate and Its Implications for the Mechanism of Oxacyclization by the Loline-Producing Iron(II)- and 2-Oxoglutarate-Dependent Oxygenase, LolO

• DOI: 10.1021/acs.biochem.4c00166
• Publication Date: 2024-06-20T04:51:15Z
• Authors: Juan Pan; Eliott S. Wenger; Chi-Yun Lin; Bo Zhang; Debangsu Sil; Irene Schaperdoth; Setareh Saryazdi; Robert B. Grossman; Carsten Krebs; J. Martin Bollinger
• Keywords: 0301 basic medicine; 03 medical and health sciences; Bacterial Proteins; Cyclization; Iron; Oxygenases; Ketoglutaric Acids; Hydroxylation

N-Acetylnorloline synthase (LolO) is one of several iron(II)- and 2-oxoglutarate-dependent (Fe/2OG) oxygenases that catalyze sequential reactions different types in the biosynthesis valuable natural products. LolO hydroxylates C2 1-exo-acetamidopyrrolizidine before coupling C2-bonded oxygen to C7 form tricyclic loline core. Each reaction requires cleavage a C–H bond by an oxoiron(IV) (ferryl) intermediate; however, carbons are targeted, carbon radicals have fates. Prior studies indicated substrate-cofactor disposition (SCD) controls site H· abstraction can affect outcome. These indications led us determine whether change SCD from first second might contribute observed reactivity switch. Whereas single ferryl complex hydroxylation was previously shown typical Mössbauer parameters, two complexes accumulate during oxacyclization has highest isomer shift seen date for such abstracts ∼ 20 times faster than does its reported off-pathway C7. The detectable competition with cyclization not enhanced 2H2O solvent, suggesting hydroxyl deprotonated prior C7–H cleavage. observations consistent coordination complex, which may reorient oxo ligand, substrate, or both positions more favorable oxacyclization.