The use of SMALPs combined to single particle cryo-electron microscopy (cryo-EM): a new approach to determine the structure of GPCRs

Supervisor: Dr. Ingrid Langer

The superfamily of GPCRs is a large and diverse family of seven transmembrane domain proteins. Because they are involved in all physiological processes, GPCRs are the largest target (30-40%) of marketed drugs and represent a major focus in research. More particularly, understanding how GPCRs work at the molecular and the cellular level is important both in terms of basic biology but also for the development of new drugs.

Major advances in the structural biology of GPCRs only came a few years ago from solving the experimental structure of the human β2 adrenergic receptor by X-ray crystallography. Although X-ray crystallography is the gold-standard technique in structural biology, it is hindered by the unpredictability of crystal formation especially for membrane protein samples. To tackle this issue, each receptor must be engineered and individually tailored, a process that can be time-consuming, and in some cases proved impossible. Simultaneously, due to important technological advances, single-particle cryo-EM has become a versatile and powerful tool to solve routinely near-atomic resolution 3D protein structures.

The main goal of the project is to implement in the laboratory an efficient method to purify functional recombinant GPCRs in order to solve their 3D structure using single particle cryo-EM. For that purpose, we propose to use a detergent-free solubilisation method. This approach, compatible with cryo-EM, relies on the use of styrene-maleic acid (SMA) co-polymers able to form small discs containing the cell membrane bilayer and termed SMALPs. As a proof of concept, we selected one GPCR routinely studied in the laboratory, namely VPAC1 (a neuropeptide receptor).

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