FRET analysis was conducted using the spectral approach established by Zheng and Zagotta. Briefly, FRET efficiency was quantified by exciting the donor (h-cisPT tryptophans) at 280 nm and measuring emission from the acceptor (danysl-PE-containing nanodiscs). The acceptor emission spectrum was isolated by subtracting the normalized tryptophan emission collected from a control sample containing only h-cisPT.