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Partial specific volume and solvent interactions of amphipol A8-35
Yann Gohon1, Georgy Pavlov, Peter Timmins
1Laboratoire de Physico-Chimie Moléculaire des Membranes Biologiques, UMR 7099, CNRS and Université Paris-7, Institut de Biologie Physico-Chimique, CNRS FRC 550, 13 rue Pierre et Marie Curie, F-75005 Paris, France.
Analytical Biochemistry
|October 21, 2004
Summary
Amphipols, used to stabilize membrane proteins, require accurate partial specific volume and effective charge determination. The sH/sD method, validated with model macromolecules, provides these crucial polymer properties for solution studies.
Area of Science:
- Biophysical Chemistry
- Polymer Science
- Membrane Protein Biochemistry
Background:
- Amphipols are essential for stabilizing membrane proteins in aqueous solutions without detergents.
- Accurate determination of amphipol properties, specifically partial specific volume (v2) and effective charge (z), is critical for studying membrane protein complexes.
Purpose of the Study:
- To accurately determine the partial specific volume (v2) and effective charge (z) of amphipols for solution studies.
- To evaluate the accuracy, advantages, and limitations of the sedimentation velocity (sH/sD) method for characterizing amphipols.
Main Methods:
- Sedimentation velocity (sH/sD method) and sedimentation equilibrium experiments to determine buoyant molar masses in H2O and D2O.
- Small-angle neutron scattering (SANS) to determine the contrast match point (CMP).
- Density measurements in H2O, D2O, and D2(18)O for a polyacrylate-based amphipol (A8-35).
Main Results:
- The sH/sD method, validated with DNA, proteins, and polysaccharides, accurately characterizes amphipol properties.
- Measurements on amphipol A8-35 provided a consistent description of its buoyancy and charge properties.
- The study highlights the importance of considering H/D exchange and counter-ion dissociation effects.
Conclusions:
- The sH/sD method is a reliable technique for determining amphipol v2 and z, crucial for membrane protein research.
- This method is particularly advantageous for analyzing heterogeneous samples.
- The findings contribute to a better understanding of amphipol behavior in solution.