Assemblies of lauryl maltose neopentyl glycol (LMNG) and LMNG-solubilized membrane proteins

Abstract

Laurylmaltose neopentylglycol (LMNG) bears two linked hydrophobic chains of equal length and two hydrophilic maltoside groups. It arouses a strong interest in the field of membrane protein biochemistry, since it was shown to efficiently solubilize and stabilize membrane proteins often better than the commonly used dodecylmaltopyranoside (DDM), and to allow structure determination of some challenging membrane proteins. However, LMNG was described to form large micelles, which could be unfavorable for structural purposes. We thus investigated its auto-assemblies and the association state of different membrane proteins solubilized in LMNG by analytical ultracentrifugation, size exclusion chromatography coupled to light scattering, centrifugation on sucrose gradient and/or small angle scattering. At high concentrations (in the mM range), LMNG forms long rods, and it stabilized the membrane proteins investigated herein, i.e. a bacterial multidrug transporter, BmrA; a prokaryotic analogous of the eukaryotic NADPH oxidases, SpNOX; an E. coli outer membrane transporter, FhuA; and the halobacterial bacteriorhodopsin, bR. BmrA, in the Apo and the vanadate-inhibited forms showed reduced kinetics of limited proteolysis in LMNG compared to DDM. Both SpNOX and BmrA display an increased specific activity in LMNG compared to DDM. The four proteins form LMNG complexes with their usual quaternary structure and with usual amount of bound detergent. No heterogeneous complexes related to the large micelle size of LMNG alone were observed. In conditions where LMNG forms assemblies of large size, FhuA crystals diffracting to 4.0 Å were obtained by vapor diffusion. LMNG large micelle size thus does not preclude membrane protein homogeneity and crystallization.