Membrane Protein Crystallization

Abstract

Hydrophobic lipids are the major component in biological membranes that serve as a boundary between two aqueous spaces in the cell body. Membrane proteins (MPs) sit within the lipidic boundary between the biovolumes and are often responsible for translocating small chemical molecules and transmitting signals from one side of the membrane to the other. MPs are usually classified into three types based on their secondary structures and location in the lipid bilayer: α-helical MPs, β-barrel MPs, and monotopic MPs. This chapter focuses on the preparation and crystallization of integral α-helical and β-barrel MPs. Protein preparation to crystallization involves three main steps: protein production, sample preparation, and crystallization. X-ray crystallography, X-ray free electron laser crystallography, and single-particle cryo-electron microscopy are all powerful tools for determining protein structures. Amphipathic detergent molecules are widely used to disguise MPs as soluble proteins and solubilize them in aqueous solutions.