Interhelical distance measurements support a hairpin conformation for Caveolin-1 in phospholipid bicelles

Previous molecular dynamics (MD) simulations of caveolin-1 (Cav1) in our labs revealed the possibility of two stable conformations of its intramembrane helices (H1 and H2). To distinguish between these two conformations, experimental intramolecular distances obtained using FRET (Forster resonance energy transfer) were integrated into the MD simulations to better define the position of these helices. Two mutants of Cav1 were generated where an acceptor fluorophore, dansyl, was positioned at the N-terminal end and center of H1 (A87C, F99C respectively), while a donor fluorophore, a native tryptophan, was positioned at the C-terminal end of H2 (W128). For the A87C W128 mutant, a distance of 22.5 {+/-} 0.3 [A] was observed while a distance of 24.4 {+/-} 0.2 [A] was observed for the F99C W128 mutant in phospholipid bicelles. These experimental FRET distances were compared to distances in MD simulations of over 100 Cav1 structures. Together these studies support that H1 and H2 adopt a hairpin conformation in bicelles.