title: A New Gd(3+) Spin Label for Gd(3+)-Gd(3+) Distance Measurements in Proteins Produces Narrow Distance Distributions.
abstract: Gd(3+) tags have been shown to be useful for performing distance measurements in biomolecules via the double electron-electron resonance (DEER) technique at Q- and W-band frequencies. We introduce a new cyclen-based Gd(3+) tag that exhibits a relatively narrow electron paramagnetic resonance (EPR) spectrum, affording high sensitivity, and which yields exceptionally narrow Gd(3+)-Gd(3+) distance distributions in doubly tagged proteins owing to a very short tether. Both the maxima and widths of distance distributions measured for tagged mutants of the proteins ERp29 and T4 lysozyme, featuring Gd(3+)-Gd(3+) distances of ca. 6 and 4 nm, respectively, were well reproduced by simulated distance distributions based on available crystal structures and sterically allowed rotamers of the tag. The precision of the position of the Gd(3+) ion is comparable to that of the nitroxide radical in an MTSL-tagged protein and thus the new tag represents an attractive tool for performing accurate distance measurements and potentially probing protein conformational equilibria.
authors.affiliation: Research School of Chemistry, Australian National University , Canberra, ACT 2601, Australia.
authors.forename: Elwy H
authors.initials: EH
authors.lastname: Abdelkader
authors.affiliation: Monash Institute of Pharmaceutical Sciences, Monash University , Parkville VIC 3052, Australia.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Lee
authors.affiliation: Department of Chemical Physics, Weizmann Institute of Science , Rehovot 76100, Israel.
authors.forename: Akiva
authors.initials: A
authors.lastname: Feintuch
authors.affiliation: Department of Chemical Physics, Weizmann Institute of Science , Rehovot 76100, Israel.
authors.forename: Marie Ramirez
authors.initials: MR
authors.lastname: Cohen
authors.affiliation: Monash Institute of Pharmaceutical Sciences, Monash University , Parkville VIC 3052, Australia.
authors.forename: James D
authors.initials: JD
authors.lastname: Swarbrick
authors.affiliation: Research School of Chemistry, Australian National University , Canberra, ACT 2601, Australia.
authors.forename: Gottfried
authors.initials: G
authors.lastname: Otting
authors.affiliation: Monash Institute of Pharmaceutical Sciences, Monash University , Parkville VIC 3052, Australia.
authors.forename: Bim
authors.initials: B
authors.lastname: Graham
authors.affiliation: Department of Chemical Physics, Weizmann Institute of Science , Rehovot 76100, Israel.
authors.forename: Daniella
authors.initials: D
authors.lastname: Goldfarb
keywords: double electron−electron resonance (DEER); electron paramagnetic resonance