Refolding and characterization of two G protein-coupled receptors purified from E. coli inclusion bodies

Unlocking GPCR-ligand interactions: Measuring binding affinities with thermal shift assay

G protein-coupled receptors (GPCRs) constitute the largest transmembrane protein superfamily, with over 800 representatives in the human genome. Recognized as pivotal targets in pharmacological research and drug discovery, these receptors play a crucial role in advancing therapeutics. Understanding the molecular mechanisms of receptor-ligand interactions is imperative for drug discovery applications. However, experimental procedures for measuring ligand binding are complicated by various factors, including the transmembrane nature of the receptors and the high cost associated with specialized instruments and consumables. Here we introduce an application of the thermal shift assay (TSA) to measuring ligand binding affinities for GPCRs. TSA is a cost-effective and user-friendly method that detects changes in protein stability induced by alterations in environmental conditions. Employing the human A2A adenosine receptor as a representative GPCR, we determined binding constants for four orthosteric ligands and allosteric sodium using three mathematical models for TSA data approximation and analysis. Models were additionally validated by two antagonists of cysteinyl leukotriene GPCR (CysLT1R), used as antiasthmatic drugs. Our results suggest that the TSA approach demonstrates a high degree of reproducibility and agreement with existing literature data, thereby affirming its suitability for investigating GPCR interactions with various types of ligands.

Protein Design Strategies for the Structural–Functional Studies of G Protein-Coupled Receptors

G protein-coupled receptors (GPCRs) are an important family of membrane proteins responsible for many physiological functions in human body. High resolution GPCR structures are required to understand their molecular mechanisms and perform rational drug design, as GPCRs play a crucial role in a variety of diseases. That is difficult to obtain for the wild-type proteins because of their low stability. In this review, we discuss how this problem can be solved by using protein design strategies developed to obtain homogeneous stabilized GPCR samples for crystallization and cryoelectron microscopy.

Wireless portable bioelectronic nose device for multiplex monitoring toward food freshness/spoilage

Monitoring food freshness/spoilage is important to ensure food quality and safety. Current methods of food quality monitoring are mostly time-consuming and labor intensive processes that require massive analytical equipment. In this study, we developed a portable bioelectronic nose (BE-nose) integrated with trace amine-associated receptor (TAAR) nanodiscs (NDs), allowing food quality monitoring via the detection of food spoilage indicators, including the biogenic amines cadaverine (CV) and putrescine (PT). The olfactory receptors TAAR13c and TAAR13d, which have specific affinities for CV and PT, were produced and successfully reconstituted in ND structures. TAAR13 NDs BE-nose-based side-gated field-effect transistor (SG-FET) system was constructed by utilizing a graphene micropattern (GM) into which two types of olfactory NDs (TAAR13c ND and TAAR13d ND) were introduced, and this system showed ultrahigh sensitivity for a limit of detection (LOD) of 1 fM for CV and PT. Moreover, the binding affinities between the TAAR13 NDs and the indicators were confirmed by a tryptophan fluorescence quenching assay and biosimulations, in which the specific binding site was confirmed. Gas-phase indicators were detected by the TAAR13 NDs BE-nose platform, and the LODs for CV and PT were confirmed to be 26.48 and 7.29 ppb, respectively. In addition, TAAR13 NDs BE-nose was fabricated with commercial gas sensors as a portable platform for the measurement of NH₃ and H₂S, multiplexed monitoring was achieved with similar performance, and the change ratio of the indicators was observed in a real sample. The integration of commercial gas sensors on a BE-nose enhanced the accuracy and reliability for the quality monitoring of real food samples. These results indicate that the portable TAAR13 NDs BE-nose can be used to monitor CV and PT over a wide range of concentrations, therefore, the electronic nose platform can be utilized for monitoring the freshness/spoilage step in various foods.