Simulation and modelling of the detergent corona around the membrane protein MhsT based on SAXS data

For membrane proteins, ab initio modelling based on a single curve of small-angle X-ray scattering (SAXS) is precluded by the presence of detergent molecules bound to the hydro­phobic region of the protein. MEMPROT was developed for the modelling of protein–detergent complexes based on the SAXS curve of the complex, and on an a priori representation of the detergent corona by an elliptical semi-torus surrounding the protein. In previous studies, MEMPROT has succeeded in modelling several membrane proteins solubilized in n-do­decyl-β-malto­pyran­oside (DDM). However, it has never been tested on proteins solubilized in other detergents. To understand whether the geometrical shape currently parametrized in MEMPROT could be applied to a broader catalogue of protein–detergent complexes, here, MEMPROT was used to model the detergent corona around the multi-hydro­phobic substrate transporter from Bacillus halodurans solubilized in four different detergents, namely DDM, n-decyl-β-malto­pyran­oside (DM), 4-cyclo­hexyl-1-butyl-β-D-maltoside (Cymal4) and decyl-maltose-neo­pentyl-glycol (DMNG). The study indicates a significant variation in detergent shapes, depending on the type of detergent. The modelling results suggest that the elliptical semi-torus with a circular closure is an excellent approximation for long-tailed detergents (DDM and DM) but leads to a slightly poorer agreement with the data for DMNG and Cymal4, which have a shorter hydro­phobic tail, smaller than the half-width of the protein hydro­phobic region. Here, for the latter, it is hypothesized that a corona with a flatter closure would be a better shape descriptor.