FIGURE 3.
(A) Spin coupling (Ω) data from our previous SDSL-EPR study using N-terminus labeled M2TM peptides in PC bilayers9 and the current study (B) using M2TMC data from Figure 2. Both data sets provide support for a conformation change due to a change in bilayer thickness. For simplicity, only two of four peptides in the tetramer are shown in the hypothetical cartoon models shown in C and D. M2 peptides could adapt to the hydrophobic thickness of the membrane either by adjusting their tilt angle with respect to the membrane normal and/or by changing the ordering of the helical bundle from a looser tetramer, where helices make some contacts with each other, to a tighter tetramer, where helix-helix associations are maximized. These two mechanisms are not mutually exclusive and they may occur in concert with one another. For simplicity, the models shown here show a simple helix tilt mechanism.