Figure 4. Possible structural changes of lipid bilayer membranes in response to tension reported by FliptR.

(a) Initial state where FliptR molecules are partially planarized in the membrane. Upon increasing tension, three structural changes could conceivably occur, namely (b) a loosening of the packing with increasing distance between less ordered lipid acyl chains, leading to FliptR deplanarization, (c) a tilting and stretching of more ordered acyl chains, which should lead to more compression of the FliptR probe and thus planarization, and (d) phase separation, in which case, FliptR molecules are more planarized in the L_o phase and less planarized in the L_d phase.