title: Designed metalloprotein stabilizes a semiquinone radical.
abstract: Enzymes use binding energy to stabilize their substrates in high-energy states that are otherwise inaccessible at ambient temperature. Here we show that a de novo designed Zn(II) metalloprotein stabilizes a chemically reactive organic radical that is otherwise unstable in aqueous media. The protein binds tightly to and stabilizes the radical semiquinone form of 3,5-di-tert-butylcatechol. Solution NMR spectroscopy in conjunction with molecular dynamics simulations show that the substrate binds in the active site pocket where it is stabilized by metal-ligand interactions as well as by burial of its hydrophobic groups. Spectrochemical redox titrations show that the protein stabilized the semiquinone by reducing the electrochemical midpoint potential for its formation via the one-electron oxidation of the catechol by approximately 400 mV (9 kcal mol(-1)). Therefore, the inherent chemical properties of the radical were changed drastically by harnessing its binding energy to the metalloprotein. This model sets the basis for designed enzymes with radical cofactors to tackle challenging chemistry.
authors.affiliation: Department of Pharmaceutical Chemistry, University of California - San Francisco, San Francisco, California 94158, USA.
authors.forename: Gözde
authors.initials: G
authors.lastname: Ulas
authors.affiliation: Department of Pharmaceutical Chemistry, University of California - San Francisco, San Francisco, California 94158, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Lemmin
authors.affiliation: Department of Pharmaceutical Chemistry, University of California - San Francisco, San Francisco, California 94158, USA.
authors.forename: Yibing
authors.initials: Y
authors.lastname: Wu
authors.affiliation: Department of Chemistry and Biochemistry, San Francisco State University, San Francisco, California 94132, USA.
authors.forename: George T
authors.initials: GT
authors.lastname: Gassner
authors.affiliation: Department of Pharmaceutical Chemistry, University of California - San Francisco, San Francisco, California 94158, USA.
authors.forename: William F
authors.initials: WF
authors.lastname: DeGrado
mesh_terms: D000595:Amino Acid Sequence; D016227:Benzoquinones / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008667:Metalloproteins / Q000737:chemistry*; D008962:Models, Theoretical; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data
chemical_list: D016227:Benzoquinones; D008667:Metalloproteins; C025232:semiquinone radicals