BAmSA: Visualising transmembrane regions in protein complexes using biotinylated amphipols and electron microscopy

Purification of Membrane Proteins Overexpressed in Saccharomyces cerevisiae

Membrane protein (MP) functional and structural characterization requires large quantities of high-purity protein for downstream studies. Barriers to MP characterization include ample overexpression, solubilization, and purification of target proteins while maintaining native activity and structure. These barriers can be overcome by utilizing an efficient purification protocol in a high-yield eukaryotic expression system such as Saccharomyces cerevisiae. S. cerevisiae offers improved protein folding and posttranslational modifications compared to prokaryotic expression systems. This chapter contains practices used to overcome barriers of solubilization and purification using S. cerevisiae that are broadly applicable to diverse membrane associated, and membrane integrated, protein targets.

Amphipathic environments for determining the structure of membrane proteins by single-particle electron cryo-microscopy

Over the past decade, the structural biology of membrane proteins (MPs) has taken a new turn thanks to epoch-making technical progress in single-particle electron cryo-microscopy (cryo-EM) as well as to improvements in sample preparation. The present analysis provides an overview of the extent and modes of usage of the various types of surfactants for cryo-EM studies. Digitonin, dodecylmaltoside, protein-based nanodiscs, lauryl maltoside-neopentyl glycol, glyco-diosgenin, and amphipols (APols) are the most popular surfactants at the vitrification step. Surfactant exchange is frequently used between MP purification and grid preparation, requiring extensive optimization each time the study of a new MP is undertaken. The variety of both the surfactants and experimental approaches used over the past few years bears witness to the need to continue developing innovative surfactants and optimizing conditions for sample preparation. The possibilities offered by novel APols for EM applications are discussed.

Advances in domain and subunit localization technology for electron microscopy

The award of the 2017 Nobel Prize in chemistry, 'for developing cryo-electron microscopy for the high-resolution structure determination of biomolecules in solution', was recognition that this method, and electron microscopy more generally, represent powerful techniques in the scientific armamentarium for atomic level structural assessment. Technical advances in equipment, software, and sample preparation, have allowed for high-resolution structural determination of a range of complex biological machinery such that the position of individual atoms within these mega-structures can be determined. However, not all targets are amenable to attaining such high-resolution structures and some may only be resolved at so-called intermediate resolutions. In these cases, other tools are needed to correctly characterize the domain or subunit orientation and architecture. In this review, we will outline various methods that can provide additional information to help understand the macro-level organization of proteins/biomolecular complexes when high-resolution structural description is not available. In particular, we will discuss the recent development and use of a novel protein purification approach, known as the the PA tag/NZ-1 antibody system, which provides numberous beneficial properties, when used in electron microscopy experimentation.