Close allies in membrane protein research: Cell-free synthesis and nanotechnology

Abstract

Membrane proteins control fundamental processes that are inherent to nearly all forms of life such as transport of molecules, catalysis, signaling, vesicle fusion, sensing of chemical and physical stimuli from the environment, and cell-cell interactions. Membrane proteins are harbored within a non-equilibrium fluid-like environment of biological membranes that separate cellular and non-cellular environments, as well as in compartmentalized cellular organelles. One of the classes of membrane proteins that will be specifically treated in this article are transport proteins of plant origin, that facilitate material and energy transfer at the membrane boundaries. These proteins import essential nutrients, export cellular metabolites, maintain ionic and osmotic equilibriums and mediate signal transduction. The aim of this article is to report on the progress of membrane protein functional and structural relationships, with a focus on producing stable and functional proteins suitable for structural and biophysical studies. We interlink membrane protein production primarily through wheat-germ cell-free protein synthesis (WG-CFPS) with the growing repertoire of membrane mimicking environments in the form of lipids, surfactants, amphipathic surfactant polymers, liposomes and nanodiscs that keep membrane proteins soluble. It is hoped that the advancements in these fields could increase the number of elucidated structures, in particular those of plant membrane proteins, and contribute to bridging of the gap between structures of soluble and membrane proteins, the latter being comparatively low.

Keywords::

• Amphipathic polymers
• biophysics
• function and structure of membrane proteins
• interactomes
• nanoparticles
• phospholipid bilayers
• membrane protein reconstitution
• transporters
• surfactants

Acknowledgements

This work was supported by the grants from the Australian Research Council and the Grains Research & Development Corporation, by the South Australian Government, and by the DP120100900 and LP120100201 grants from the Australian Research Council awarded to MH. We are grateful to the members of the Structural Biology Group at the Australian Centre for Plant Functional Genomics of the University of Adelaide, who over the years have contributed to WG-CFPS and nanotechnology.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.