Dependence of Micelle Size and Shape on Detergent Alkyl Chain Length and Head Group

Abstract

Micelle-forming detergents provide an amphipathic environment that can mimic lipid bilayers and are important tools for solubilizing membrane proteins for functional and structural investigations in vitro. However, the formation of a soluble protein-detergent complex (PDC) currently relies on empirical screening of detergents, and a stable and functional PDC is often not obtained. To provide a foundation for systematic comparisons between the properties of the detergent micelle and the resulting PDC, a comprehensive set of detergents commonly used for membrane protein studies are systematically investigated. Using small-angle X-ray scattering (SAXS), micelle shapes and sizes are determined for phosphocholines with 10, 12, and 14 alkyl carbons, glucosides with 8, 9, and 10 alkyl carbons, maltosides with 8, 10, and 12 alkyl carbons, and lysophosphatidyl glycerols with 14 and 16 alkyl carbons. The SAXS profiles are well described by two-component ellipsoid models, with an electron rich outer shell corresponding to the detergent head groups and a less electron dense hydrophobic core composed of the alkyl chains. The minor axis of the elliptical micelle core from these models is constrained by the length of the alkyl chain, and increases by 1.2–1.5 Å per carbon addition to the alkyl chain. The major elliptical axis also increases with chain length; however, the ellipticity remains approximately constant for each detergent series. In addition, the aggregation number of these detergents increases by ∼16 monomers per micelle for each alkyl carbon added. The data provide a comprehensive view of the determinants of micelle shape and size and provide a baseline for correlating micelle properties with protein-detergent interactions.

Multifunctional-layered materials for creating membrane-restricted nanodomains and nanoscale imaging

“…Small Angle X-ray Scattering (SAXS) of micelles produced from commonly used detergents at concentrations exceeding critical micelle concentration (CMC) revealed that micelles tend to form spherical or elliptic (prolate or oblate) shapes at nanometre length scales. 23 lm; average minor dimension, a $ 0.834 6 0.084 lm; aspect ratio (a/b) $ 0.476 6 0.049) with an aspect ratio close to that of the DDM micelles reported previously. Although final shape of a micelle structure depends on detergent concentration, temperature, length of the carbon chain, hydrophobicity of the environment, etc., the aspect ratio of the structure seems to be almost conserved.…”

“…Investigating the morphology of bicelles allows identifying suitable conditions that produces stable and soluble protein-detergent complexes 23 and lipid-detergent bicelle complexes 24 for membrane proteins crystallography. Small Angle X-ray Scattering (SAXS) of micelles produced from commonly used detergents at concentrations exceeding critical micelle concentration (CMC) revealed that micelles tend to form spherical or elliptic (prolate or oblate) shapes at nanometre length scales.…”

Controlling Carbon-Nanotube—Phospholipid Solubility by Curvature-Dependent Self-Assembly

“…Due to the high spontaneus curvature of LPC, LPC micelles have small aggregation numbers of approximately 100-200 molecules. 83 Aggregates of this size readily adsorb which means the surface coverage is likely to rapidly saturate. This speculation is supported by the observed LPC adsorption behavior in our simulations and the excellent agreement between our simulation and experiments (LPC surface coverage of 1.61 LPC/nm 2 in the simulations and 1.51 LPC/nm 2 in Ref.…”

Structural and Dynamic Insights of the Interaction between Tritrpticin and Micelles: An NMR Study

“…Micelle-forming detergents provide amphipathic environments similar to those found in lipid bilayers and biomembranes. Micelles have different shapes and sizes determined by the chemical nature of their headgroups and the length of their hydrophobic tails (23,24). Physicochemical conditions such as temperature, solutes, and concentration can also affect micellar structure and eventually influence the conformation of bound proteins or peptides, especially the latter.…”

“…Our study focuses on TRP3 accommodation at the hydrophilic/ hydrophobic interface of micelles and subsequent events. The structure and dynamics of TRP3 were examined in the presence of micelles of different chemical nature: zwitterionic (lysolauroylphosphatidylcholine 1-lauroyl-2-hydroxy-sn-glycero-3-phosphocholine (LLPC), n-dodecylphosphocholine (DPC), and N-dodecyl-N,N-(dimethylammonio) butyrate (DDMAB), anionic 1-myristoyl-2-hydroxy-sn-glycero-3-phospho-(1 0 -rac-glycerol) (LMPG), and nonionic (octylglucoside (OG)) (23,24,(31)(32)(33)(34)(35). The conformational ensemble was evaluated during detergent titration and it was found that the peptide interacts via conformational selection.…”