Chemical Synthesis of a Full-Length G-Protein-Coupled Receptor β-Adrenergic Receptor with Defined Modification Patterns at the C-Terminus.

The β-adrenergic receptor (βAR) is a G-protein-coupled receptor (GPCR) that responds to the hormone adrenaline and is an important drug target in the context of respiratory diseases, including asthma. βAR function can be regulated by post-translational modifications such as phosphorylation and ubiquitination at the C-terminus, but access to the full-length βAR with well-defined and homogeneous modification patterns critical for biochemical and biophysical studies remains challenging. Here, we report a practical synthesis of differentially modified, full-length βAR based on a combined native chemical ligation (NCL) and sortase ligation strategy. An array of homogeneous samples of full-length βARs with distinct modification patterns, including a full-length βAR bearing both monoubiquitination and octaphosphorylation modifications, were successfully prepared for the first time. Using these homogeneously modified full-length βAR receptors, we found that different phosphorylation patterns mediate different interactions with β-arrestin1 as reflected in different agonist binding affinities. Our experiments also indicated that ubiquitination can further modulate interactions between βAR and β-arrestin1. Access to full-length βAR with well-defined and homogeneous modification patterns at the C-terminus opens a door to further in-depth mechanistic studies into the structure and dynamics of βAR complexes with downstream transducer proteins, including G proteins, arrestins, and GPCR kinases.