Small-residue-mediated interhelical packings are ubiquitously found in helical membrane proteins, although their interaction dynamics and lipid dependence remain mostly uncharacterized. We used a single-pair FRET technique to examine the effect of a GXXXG motif on the association of denovo designed (AALALAA) 3 helices in liposomes. Dimerization occurred with sub-second lifetimes, which was abolished by cholesterol. Utilizing the nearly instantaneous time-resolution of 2D IR spectroscopy, parallel and antiparallel helix associations were identified by vibrational couplings across helices at their interface. Taken together, the data illustrate that the GXXXG motif controls helix packing but still allows for a dynamic and lipid-regulated oligomeric state.
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AbstractUnique interaction inside membrane: Model transmembrane helices containing a GXXXG motif were synthesized to explore interplay of the motif and lipid composition on the intramembrane helix associations. Single-pair FRET with controlled association topology and isotope-edited 2D-IR experiments revealed the dynamic nature, distinct interfaces, and high cholesterol sensitivity of the GXXXG-mediated interactions, which can actively regulate the functions of membrane proteins.