Lipid-protein nanodiscs as reference medium in detergent screening for high-resolution NMR studies of integral membrane proteins.

The choice of a suitable detergent-based membrane mimetic is of crucial importance for high-resolution NMR studies of membrane proteins. The present report describes a new approach of detergent screening. It is based on the comparison of 2D (1)H,(15)N-correlation spectra of a protein in a membrane-bilayer "reference" medium and in "trial" detergent-based environments. The proposed "reference" medium is the lipid-protein nanodisc (LPN) representing nanoscale phospholipid bilayers wrapped around by apolipoprotein A-1. The set of zwitterionic (DPC, DMPC/DHPC), anionic (SDS, LMPG, LPPG), and weakly cationic (LDAO) detergent-based media was screened for their ability to represent the native structure of the isolated voltage-sensing domain (VSD) of the archaeal potassium channel KvAP. The VSD/LPN complexes composed of saturated zwitterionic (DMPC), anionic (DMPG), or a mixture of unsaturated differently charged (POPC/DOPG, 3:1) lipids were used as reference. All assayed detergent media demonstrate similar CD spectra of the domain with a high level (approximately 60%) of overall helicity but different 2D NMR spectra. Using the reference spectrum of the VSD in LPN, we were able to choose the detergent composition in which the membrane-like structure of the VSD is preserved.