Figure 3.
The hydrophobic segments of PopD did not adopt a typical transmembrane orientation in hetero-complexes. Multiple residues in segments H1 and H2 were replaced by Cys and labeled with the environment-sensitive probe NBD. Each single NBD-labeled PopD was premixed with a 10 times molar excess of PopB WT before incubation with liposomes. Reported data correspond to the mean of two independent measurements and error bars indicate the range. A, λmax of NBD attached to the indicated residue in segment H2. B, λmax of NBD attached to the indicated residue in segment H1. C, average τ; for NBD-labeled residues in segment H2. D, average τ for NBD-labeled residues in segment H1. The λmax and τ for NBD in water (red lines) and NBD-cholesterol in liposomes (blue lines) serve as references for expected values of λmax and τ for NBD located in a polar or hydrophobic environment, respectively.