Integral membrane protein/amphipol complexes and high-resolution solution-state NMR spectroscopy.

2_Size of membrane protein/amphipol complexes.

The complexes appear slightly bigger than membrane protein/detergent complexes, based on estimates of the overall correlation time, τc . For instance, the correlation time of A8-35-trapped OmpX (31 ns) (Catoire et al (2010b)) lies between that of OmpX in solutions of dihexanoylphosphatidylcholine (24 ns) (Lee et al (2006)) and that of OmpX inserted into small isotropic bicelles (35 ns) (Lee et al (2008)). The slightly larger size of membrane protein/amphipol complexes compared to those formed with the most favorable detergents does not preclude obtaining high-resolution spectra nor achieving enough sensitivity to perform 3D experiments. Indeed, 3D 15N-edited [1H,1H]-HSQC-NOESY spectra have been collected to explore dipolar interactions between KpOmpA (from Klebsiella pneumoniae) and A8-35 (M. Renault & A. Milon, unpublished data).