How Do Branched Detergents Stabilize GPCRs in Micelles?

Abstract

The structural and functional properties of G protein-coupled receptors (GPCRs) are often studied in a detergent micellar environment, but many GPCRs tend to denature or aggregate in short alkyl-chain detergents. In our previous work (J. Am. Chem. Soc., 2016), we showed that GPCRs in alkyl-glucosides were highly dynamic resulting in penetration of detergent molecules between transmembrane α-helices, which is the initial step in receptor denaturation. Although this was not ob-served for GPCRs in dodecylmaltoside (DDM, also known as laurylmaltoside), even this detergent is not mild enough to pre-serve the integrity of many GPCRs during purification. Lauryl Maltose Neopentylglycol (LMNG) detergents such as LMNG have been found to have significant advantages for purifying GPCRs in a native state as they impart more stability to the receptor than DDM. To gain insights into how they stabilize GPCRs, we used atomistic molecular dynamics simulations of wild type adenosine A_2A receptor (WT-A_2AR), thermostabilized A_2AR (tA_2AR) and wild type β₂-adrenoceptor (β₂AR) in a variety of detergents (LMNG, DMNG, OGNG and DDM). Analysis of MD simulations of tA_2AR in LMNG, DMNG and OGNG showed that this series of detergents behaved very similarly to the analogous series of detergents DDM, DM and OG in our previous study. However, there was a striking difference comparing the behavior of LMNG compared to DDM. LMNG showed considerably less motion than DDM, which resulted in enhanced density of the aliphatic chains around the hydrophobic regions of the receptor and considerably more hydrogen bond formation between the head groups. This contributed to enhanced interaction energies between both detergent molecules and between the receptor and detergent, explaining the enhanced stability of GPCRs purified in this detergent. Our results provide a rational foundation on which to develop further variants of detergents that can stabilize even the most unstable membrane proteins.