Heavy Atom Detergent/Lipid Combined X-ray Crystallography for Elucidating the Structure-Function Relationships of Membrane Proteins.

Shinya Hanashima,Eiichi Mizohata,Takanori Nakane

doi:10.3390/membranes11110823

Abstract

Membrane proteins reside in the lipid bilayer of biomembranes and the structure and function of these proteins are closely related to their interactions with lipid molecules. Structural analyses of interactions between membrane proteins and lipids or detergents that constitute biological or artificial model membranes are important for understanding the functions and physicochemical properties of membrane proteins and biomembranes. Determination of membrane protein structures is much more difficult when compared with that of soluble proteins, but the development of various new technologies has accelerated the elucidation of the structure-function relationship of membrane proteins. This review summarizes the development of heavy atom derivative detergents and lipids that can be used for structural analysis of membrane proteins and their interactions with detergents/lipids, including their application with X-ray free-electron laser crystallography.

Highlights

All cellular organisms have biomembranes composed of lipids, which form a boundary between the cell cytoplasm and the surrounding extracellular environment and organize complex structures inside the cell to construct cellular organelles [1]
Membrane proteins localize in the lipid bilayer of biomembranes and play a variety of important functions such as transport of various substances between the inside and outside of the cell, signal transduction, energy synthesis, and cell adhesion
Elucidation of the structure and function of membrane proteins including their interactions with lipids at the molecular level is essential both from the perspective of basic science to understand the mechanisms of life and from the perspective of medical applications

Summary

Introduction

All cellular organisms have biomembranes composed of lipids, which form a boundary between the cell cytoplasm and the surrounding extracellular environment and organize complex structures inside the cell to construct cellular organelles [1]. Advancing synchrotron radiation facilities and beamline technologies have facilitated the determination of crystal structures of membrane proteins This trend will continue with the development of fourth-generation synchrotron radiation sources, including X-ray free-electron laser (XFEL) facilities [8]. Isomorphous replacement methods use the difference in reflection intensities between the native crystal and the heavy atom-labeled derivative crystal to determine the phases, whereas the anomalous diffraction method uses anomalous differences between Bijvoet pairs [9] Both methods require accurate measurement of small intensity differences. The development of heavy atom labeled protein ligands is needed that bind various membrane proteins and facilitate drawing electron density maps efficiently from X-ray diffraction data to reveal threedimensional structures. We discuss the potential of combining recently developed XFEL crystallography with heavy atom detergents/lipids to understand the structure-function relationship of membrane proteins and their interactions with detergents/lipids

Heavy Atom Labeled Protein Ligands

Halogens

Selenium

De Novo Phasing in SFX

De Novo Phasing with the HAD13a Detergent

Conclusions