Merging In-Solution X-ray and Neutron Scattering Data Allows Fine Structural Analysis of Membrane-Protein Detergent Complexes.

Gaëtan Dias Mirandela,Felix M Strnad,Arnaud Javelle,Tim Rasmussen,Giulia Tamburrino,Miloš T Ivanović,Ulrich Zachariae,Jochen S Hub,Frank Gabel,Paul A Hoskisson,Olwyn Byron

doi:10.1021/acs.jpclett.8b01598

Abstract

In-solution small-angle X-ray and neutron scattering (SAXS/SANS) have become popular methods to characterize the structure of membrane proteins, solubilized by either detergents or nanodiscs. SANS studies of protein-detergent complexes usually require deuterium-labeled proteins or detergents, which in turn often lead to problems in their expression or purification. Here, we report an approach whose novelty is the combined analysis of SAXS and SANS data from an unlabeled membrane protein complex in solution in two complementary ways. First, an explicit atomic analysis, including both protein and detergent molecules, using the program WAXSiS, which has been adapted to predict SANS data. Second, the use of MONSA which allows one to discriminate between detergent head- and tail-groups in an ab initio approach. Our approach is readily applicable to any detergent-solubilized protein and provides more detailed structural information on protein-detergent complexes from unlabeled samples than SAXS or SANS alone.

Highlights

I ntegral membrane proteins form the entry and exit routes for nutrients, metabolic waste and drugs in biological cells, and they are involved in key steps of signaling and energy transduction
In-solution small-angle X-ray and neutron scattering (SAXS/SANS) have become popular methods to characterize the structure of membrane proteins, solubilized by either detergents or nanodiscs
Our approach is readily applicable to any detergent-solubilized protein and provides more detailed structural information on protein−detergent complexes from unlabeled samples than SAXS or SANS alone

Summary

The Journal of Physical Chemistry Letters

Letter that combines SAXS and SANS from unlabeled (i.e., nondeuterated) proteins and/or detergent samples to obtain detailed structural information on protein−detergent complexes. It is widely recognized that cryo-electron microscopy (cryo-EM) will revolutionize the structural analysis of membrane proteins in the near future.[21,22] It is our belief that a hybrid approach, combining in solution SAS techniques, in silico modeling, and cryo-EM will allow for better tracking and description of conformational changes of membrane proteins in solution, induced by ligand or cofactor binding In this context, it was important to account accurately for the bound detergent molecules, which is greatly improved by combining SAXS and SANS data at various contrasts. Our multiphase analysis, which merges SAXS and SANS data, without using deuterated protein or detergent, allowed us to obtain unprecedented structural information on the phase density of the detergent, in particular to distinguish head- and tail-groups in the assembled membrane protein−detergent complexes.

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