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. 2008 Jun 27;95(6):2849–2858. doi: 10.1529/biophysj.108.133629

FIGURE 1.

FIGURE 1

(A) R1 spin-label side chain is incorporated into proteins by derivatizing single cysteines with the MTSL. (B) Model of Escherichia coli vitamin B-12 transport protein BtuB (Protein Data Bank identification, 1NQE (24)). The BtuB is structurally homologous to other TonB-dependent transporters, and is based on a β-barrel consisting of 22 antiparallel β-strands, with an N-terminal core domain that fills the interior of the barrel (51). Shaded region indicates the approximate location of the membrane bilayer (33). The spin-labeled side chain, R1, has been incorporated into over 30 sites on β-strands 2, 3, and 7, which are highlighted. Several labeled sites are shown: residues 150 and 156 on strand 2, residues 168 and 172 on strand 3, and residues 265 and 275 on strand 7.