Radical Stabilization Is Crucial in the Mechanism of Action of Lysine 5,6-Aminomutase: Role of Tyrosine-263α As Revealed by Electron Paramagnetic Resonance Spectroscopy

• Published in: Journal of the American Chemical Society Vol. 133; no. 43; pp. 17152 - 17155
• Main Authors: Chen, Yung-Han, Maity, Amarendra N, Pan, Yu-Chiang, Frey, Perry A, Ke, Shyue-Chu
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 02.11.2011
• Subjects: Crystallography, X-Ray; Electron Spin Resonance Spectroscopy; Free Radicals - chemistry; Free Radicals - metabolism; Intramolecular Transferases - chemistry; Intramolecular Transferases - metabolism; Models, Molecular; Molecular Structure; Stereoisomerism; Tyrosine - chemistry; Tyrosine - metabolism
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja207766c

Adenosylcobalamin- and pyridoxal-5′-phosphate-dependent lysine 5,6-aminomutase utilizes free radical intermediates to mediate 1,2-amino group rearrangement, during which an elusive high-energy aziridincarbinyl radical is proposed to be central in the mechanism of action. Understanding how the enzyme participates in stabilizing any of the radical intermediates is fundamentally significant. Y263F mutation abolished the enzymatic activity. With isotope-edited EPR methods, the roles of the Tyr263α residue in the putative active site are revealed. The Tyr263α residue stabilizes a radical intermediate, which most likely is the aziridincarbinyl radical, either by acting as a spin-relay device or serving as an anchor for the pyridine ring of pyridoxal-5′-phosphate through aromatic π-stacking interactions during spin transfer. The Tyr263α residue also protects the radical intermediate from interception by molecular oxygen. This study supports the proposed reaction mechanism, including the aziridincarbinyl radical, which has eluded detection for more than two decades.