Glyco-steroidal amphiphiles (GSAs) for membrane protein structural study

Trends in the Diversification of the Detergentome

Detergents are amphiphilic molecules that serve as enabling steps for today's world applications. The increasing diversity of the detergentome is key to applications enabled by detergent science. Regardless of the application, the optimal design of detergents is determined empirically, which leads to failed preparations, and raising costs. To facilitate project planning, here we review synthesis strategies that drive the diversification of the detergentome. Synthesis strategies relevant for industrial and academic applications include linear, modular, combinatorial, bio-based, and metric-assisted detergent synthesis. Scopes and limitations of individual synthesis strategies in context with industrial product development and academic research are discussed. Furthermore, when designing detergents, the selection of molecular building blocks, i. e., head, linker, tail, is as important as the employed synthesis strategy. To facilitate the design of safe-to-use and tailor-made detergents, we provide an overview of established head, linker, and tail groups and highlight selected scopes and limitations for applications. It becomes apparent that most recent contributions to the increasing chemical diversity of detergent building blocks originate from the development of detergents for membrane protein studies. The overview of synthesis strategies and molecular blocks will bring us closer to the ability to predictably design and synthesize optimal detergents for challenging future applications.

Micelle Formation in Aqueous Solutions of the Cholesterol-Based Detergent Chobimalt Studied by Small-Angle Scattering

The structure and interaction parameters of the water-soluble cholesterol-based surfactant, Chobimalt, are investigated by small-angle neutron and X-ray scattering techniques. The obtained data are analyzed by a model-independent approach applying the inverse Fourier transformation procedure as well as considering a model fitting procedure, using a core-shell form factor and hard-sphere structure factor. The analysis reveals the formation of the polydisperse spherical or moderately elongated ellipsoidal shapes of the Chobimalt micelles with the hard sphere interaction in the studied concentration range 0.17-6.88 mM. The aggregation numbers are estimated from the micelle geometry observed by small-angle scattering and are found to be in the range of 200-300. The low pH of the solution does not have a noticeable effect on the structure of the Chobimalt micelles. The critical micelle concentrations of the synthetic surfactant Chobimalt in water and in H₂O-HCl solutions were obtained according to fluorescence measurements as ~3 μM and ~2.5 μM, respectively. In-depth knowledge of the basic structural properties of the detergent micelles is necessary for further applications in bioscience and biotechnology.

Non-ionic cholesterol-based additives for the stabilization of membrane proteins

We report herein the synthesis of two non-ionic amphiphiles with a cholesterol hydrophobic moiety that can be used as chemical additives for biochemical studies of membrane proteins. They were designed to show a high similarity with the planar steroid core of cholesterol and small-to-medium polar head groups attached at the C3 position of ring-A on the sterol skeleton. The two Chol-Tris and Chol-DG have a Tris-hydroxymethyl and a branched diglucose polar head group, respectively, which provide them sufficient water solubility when mixed with the "gold standard" detergent n-Dodecyl-β-D-Maltoside (DDM). The colloidal properties of these mixed micelles were investigated by means of surface tension (SFT) measurements and dynamic light scattering (DLS) experiments and showed the formation of globular micelles of about 8 nm in diameter with a critical micellar concentration of 0.20 mM for DDM:Chol-DG and 0.22 mM for DDM:Chol-Tris. We showed that mixed micelles do not alter the extraction potency of a G-protein coupled receptor (GPCR): the human adenosine A2A receptor (A_2AR). The thermostabilizing effect of the mixed micelles was confirmed on two GPCRs, A_2AR and the growth hormone secretagogue receptor (GHSR). Finally, these two mixed micelles were found suitable for the purification of an active form of A_2AR which remained able to bind two ligands of different class i.e. the specific agonist CGS-21680 and the specific inverse agonist ZM-241385. This suggests that Chol-Tris and Chol-DG may be used as a non-ionic alternative to the cholesteryl hemisuccinate (CHS) stabilizing agent.