QTY code designed thermostable and water-soluble chimeric chemokine receptors with tunable ligand affinity

• Published in: Proceedings of the National Academy of Sciences - PNAS 2019-12, Vol.116 (51), p.25668-25676
• Main Authors: Qing, Rui, Han, Qiuyi, Skuhersky, Michael, Chung, Haeyoon, Badr, Myriam, Schubert, Thomas, Zhang, Shuguang
• Format: Article
• Language: English
• Subjects: Affinity; Aqueous solutions; Arginine; Biological Sciences; CCR5 protein; Chemokine receptors; Chemokines; Computational Biology - methods; CXCL12 protein; CXCR4 protein; Design; Detergents; E coli; Heat treatment; Humans; Immunology; Ligands; Models, Molecular; PNAS Plus; Protein Binding; Protein Engineering - methods; Receptors; Receptors, Chemokine - chemistry; Receptors, Chemokine - genetics; Receptors, Chemokine - metabolism; Recombinant Proteins - chemistry; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; Sequence Alignment; Solubility; Thermal stability; Water
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1909026116

Chemokine receptors are of great interest as they play a critical role in many immunological and pathological processes. The ability to study chemokine receptors in aqueous solution without detergent would be significant because natural receptors require detergents to become soluble. We previously reported using the QTY code to design detergent-free chemokine receptors. We here report the design of 2 detergent-free chimeric chemokine receptors that were experimentally unattainable in detergent solution. We designed chimeric receptors by switching the N terminus and 3 extracellular (EC) loops between different receptors. Specifically,we replaced the N terminus and 3 EC loops of CCR5QTY with the N terminus and 3 EC loops of CXCR4. The ligand for CXCR4; namely CXCL12, binds to the chimeric receptor CCR5QTY (7TM)-CXCR4 (N terminus+3 EC loops), but with lower affinity compared to CXCR4; the CCL5 ligand of CCR5 binds the chimeric receptor with ∼20× lower affinity. The chimeric design helps to elucidate the mechanism of native receptor-ligand interaction. We also show that all detergent-free QTY-designed chemokine receptors, expressed in Escherichia coli, bind to their respective chemokines with affinities in the nanomolar (nM) range, similar to the affinities of native receptors and SF9-produced QTY variants. These QTY-designed receptors exhibit remarkable thermostability in the presence of arginine and retain ligand-binding activity after heat treatment at 60 °C for 4 h and 24 h, and at 100 °C for 10 min. Our design approach enables affordable scale-up production of detergent-free QTY variant chemokine receptors with tunable functionality for various uses.