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  • Title: Determining the oligomeric structure of proteorhodopsin by Gd3+ -based pulsed dipolar spectroscopy of multiple distances.
    Author: Edwards DT, Huber T, Hussain S, Stone KM, Kinnebrew M, Kaminker I, Matalon E, Sherwin MS, Goldfarb D, Han S.
    Journal: Structure; 2014 Nov 04; 22(11):1677-86. PubMed ID: 25438671.
    Abstract:
    The structural organization of the functionally relevant, hexameric oligomer of green-absorbing proteorhodopsin (G-PR) was obtained from double electron-electron resonance (DEER) spectroscopy utilizing conventional nitroxide spin labels and recently developed Gd3+ -based spin labels. G-PR with nitroxide or Gd3+ labels was prepared using cysteine mutations at residues Trp58 and Thr177. By combining reliable measurements of multiple interprotein distances in the G-PR hexamer with computer modeling, we obtained a structural model that agrees with the recent crystal structure of the homologous blue-absorbing PR (B-PR) hexamer. These DEER results provide specific distance information in a membrane-mimetic environment and across loop regions that are unresolved in the crystal structure. In addition, the X-band DEER measurements using nitroxide spin labels suffered from multispin effects that, at times, compromised the detection of next-nearest neighbor distances. Performing measurements at high magnetic fields with Gd3+ spin labels increased the sensitivity considerably and alleviated the difficulties caused by multispin interactions.
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