Designing Mixed Detergent Micelles for Uniform Neutron Contrast

Micelle-forming detergents provide an amphipathic environment that mimics lipid bilayers and are important tools used to solubilize and stabilize membrane proteins in solution for in vitro structural investigations. Small-angle neutron scattering (SANS) at the neutron contrast match point of detergent molecules allows observing the signal from membrane proteins unobstructed by contributions from the detergent. However, we show that even for a perfectly average-contrast matched detergent there arises significant core-shell scattering from the contrast difference between aliphatic detergent tails and hydrophilic head groups. This residual signal interferes with interpreting structural data of membrane proteins. This complication is often made worse by the presence of excess empty (protein-free) micelles. We present an approach for the rational design of mixed micelles containing a deuterated detergent analog, which eliminates neutron contrast between core and shell and allows the micelle scattering to be fully contrast-matched to unambiguously resolve membrane protein structure using solution SANS.