title: Direct Observation of Nanosecond Water Exchange Dynamics at a Protein Metal Site.
abstract: Nanosecond ligand exchange dynamics at metal sites within proteins is essential in catalysis, metal ion transport, and regulatory metallobiochemistry. Herein we present direct observation of the exchange dynamics of water at a Cd2+binding site within two de novo designed metalloprotein constructs using111mCd perturbed angular correlation (PAC) of γ-rays and113Cd NMR spectroscopy. The residence time of the Cd2+-bound water molecule is tens of nanoseconds at 20 °C in both proteins. This constitutes the first direct experimental observation of the residence time of Cd2+coordinated water in any system, including the simple aqua ion. A Leu to Ala amino acid substitution ∼10 Å from the Cd2+site affects both the equilibrium constant and the residence time of water, while, surprisingly, the metal site structure, as probed by PAC spectroscopy, remains essentially unaltered. This implies that remote mutations may affect metal site dynamics, even when structure is conserved.
authors.affiliation: Department of Chemistry, University of Copenhagen , Universitetsparken 5, 2100 København Ø, Denmark.
authors.forename: Monika
authors.initials: M
authors.lastname: Stachura
authors.affiliation: Department of Chemistry, University of Michigan , Ann Arbor, Michigan 48109-1055, United States.
authors.forename: Saumen
authors.identifier: 0000-0002-9256-2769
authors.initials: S
authors.lastname: Chakraborty
authors.affiliation: CERN, 1211 Geneva 23, Switzerland.
authors.forename: Alexander
authors.initials: A
authors.lastname: Gottberg
authors.affiliation: Department of Chemistry, University of Michigan , Ann Arbor, Michigan 48109-1055, United States.
authors.forename: Leela
authors.initials: L
authors.lastname: Ruckthong
authors.affiliation: Department of Chemistry, University of Michigan , Ann Arbor, Michigan 48109-1055, United States.
authors.forename: Vincent L
authors.identifier: 0000-0002-3234-4698
authors.initials: VL
authors.lastname: Pecoraro
authors.affiliation: Department of Chemistry, University of Copenhagen , Universitetsparken 5, 2100 København Ø, Denmark.
authors.forename: Lars
authors.initials: L
authors.lastname: Hemmingsen
mesh_terms: D002104:Cadmium / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D011506:Proteins / Q000737:chemistry*; D013997:Time Factors; D014867:Water / Q000737:chemistry*
chemical_list: D008024:Ligands; D011506:Proteins; D002104:Cadmium; D014867:Water