Solution-State 17O Quadrupole Central-Transition NMR Spectroscopy in the Active Site of Tryptophan Synthase

• Published in: Angewandte Chemie 2016-01, Vol.128 (4), p.1372-1376
• Main Authors: Young, Robert P., Caulkins, Bethany G., Borchardt, Dan, Bulloch, Daryl N., Larive, Cynthia K., Dunn, Michael F., Mueller, Leonard J.
• Format: Article
• Language: English
• Subjects: Enzyme; Homogene Katalyse; Ligasen; NMR-Spektroskopie; Proteine
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.201508898

Oxygen is an essential participant in the acid–base chemistry that takes place within many enzyme active sites, yet has remained virtually silent as a probe in NMR spectroscopy. Here, we demonstrate the first use of solution‐state 17O quadrupole central‐transition NMR spectroscopy to characterize enzymatic intermediates under conditions of active catalysis. In the 143 kDa pyridoxal‐5′‐phosphate‐dependent enzyme tryptophan synthase, reactions of the α‐aminoacrylate intermediate with the nucleophiles indoline and 2‐aminophenol correlate with an upfield shift of the substrate carboxylate oxygen resonances. First principles calculations suggest that the increased shieldings for these quinonoid intermediates result from the net increase in the charge density of the substrate–cofactor π‐bonding network, particularly at the adjacent α‐carbon site. Enzymatische Reaktionen: Mehrere Intermediate des Tryptophan‐Synthase‐Reaktionscyclus wurden mittels 17O‐Quadrupol‐Zentralübergangs‐NMR‐Spektroskopie untersucht. Das Bild zeigt das 17O‐Lösungs‐NMR‐Spektrum des kinetisch kompetenten α‐Aminoacrylatintermediats dem aktiven Zentrum der β‐Untereinheit überlagert.