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. Author manuscript; available in PMC: 2012 Oct 18.
Published in final edited form as: Biochemistry. 2011 Sep 22;50(41):8792–8803. doi: 10.1021/bi200971x

Figure 1.

Figure 1

a) Model for the spin-labeled side chain R1 obtained by derivatization with an MTSL spin label. Five rotatable bonds link the R1 spin label to the protein backbone, but motions that average the nitroxide magnetic interactions are often dominated by motion about χ4 and χ5 (see text). b) Model of BtuB (PDB ID: 1NQH (24)) showing the position of 10 Cα carbons that have been spin-labeled with the side chain R1. Previous work (19) indicates that when reconstituted into POPC bilayers, sites near the aqueous solvent interface c) tend to yield EPR spectra that are multicomponent (yellow spheres), whereas at sites in the membrane interior d) yield EPR spectra that are near the rigid-limit (red spheres). All spectra are 100 Gauss scans, and normalized to equivalent spin numbers, except amplitudes of the spectra in d) are scaled by a factor of 1.5. The arrows in d) indicate the positions of the hyperfine extrema in the EPR spectrum, which are not averaged in rigid-limit EPR spectra.