Biosynthesis and NMR spectroscopic studies of large C-terminal fragments of human Y4 receptor

Abstract

G protein-coupled receptors (GPCRs) belong to a group of alpha-helical transmembrane proteins (TMPs) that are constantly involved in triggering vital biochemical responses. These receptors exist in all eukaryotic organisms, very diverse in nature and especially in humans, almost 800 varieties of genes were identified that code for these TMPs. GPCRs totally constitute only 1% of the total cellular proteins, but they mediate many vital functions of immense pharmacological significance. Almost 50% of the drugs on the market and in research target these receptors with therapeutic implication against many diseases. The major role of GPCRs is to broadcast a signal across the cellular membrane. GPCRs function by receiving an extracellular signal from ions, photons, small organic molecules, peptides, and entire proteins (for example hormones) resulting in conformational changes that affects the interacting G-proteins inside the cells. After receiving the signal G-proteins dissociate from the GPCRs, split into two subunits that trigger a cascade of downstream signaling events. It is important to note that the fundamental event triggered by ligand binding is a conformational change, which is exploited by many drugs. The relationship between structure and biological action is of great interest to tackle existing diseases or disorders because it allows designing drugs that will interfere with GPCR signaling.
In humans, approximately 15% of all genes code for GPCRs, but the function of most of them has not been discovered yet. For those the function is known, structural information is limited. Even with the present advanced technologies, characterizing these receptors at atomic-resolution is extremely challenging because of some of their properties such as their hydrophobic nature, low natural abundance, high flexibility and the lack of finding an ideal membrane mimic for them.
In my first chapter, I introduce the properties of these receptors and subsequently elaborate on the recent developments in trying to overcome low expression levels by using heterologous strains. I conclude the chapter by discussing the possibility to use different membrane mimetics that are suitable for reconstituting TMPs for biophysical analysis.