QTY code enables design of detergent-free chemokine receptors that retain ligand-binding activities

Abstract

Structure and function studies of membrane proteins, particularly G protein-coupled receptors and multipass transmembrane proteins, require detergents. We have devised a simple tool, the QTY code (glutamine, threonine, and tyrosine), for designing hydrophobic domains to become water soluble without detergents. Here we report using the QTY code to systematically replace the hydrophobic amino acids leucine, valine, isoleucine, and phenylalanine in the seven transmembrane α-helices of CCR5, CXCR4, CCR10, and CXCR7. We show that QTY code-designed chemokine receptor variants retain their thermostabilities, α-helical structures, and ligand-binding activities in buffer and 50% human serum. CCR5, CXCR4, and CXCR7 also bind to HIV coat protein gp41-120. Despite substantial transmembrane domain changes, the detergent-free QTY variants maintain stable structures and retain their ligand-binding activities. We believe the QTY code will be useful for designing water-soluble variants of membrane proteins and other water-insoluble aggregated proteins.

Discovery of the first self‐assembling peptide, study of peptide dynamic behaviors, and G protein‐coupled receptors using an Aviv circular dichroism spectropolarimeter

“…In other work, we used CD for studying integral membrane proteins, particularly G protein‐coupled receptors (GPCRs), including olfactory receptors, formyl peptide receptors, and trace amine associated receptors (Figures ) . These proteins are predominately composed of seven transmembrane α‐helical segments.…”

“…Gln (Q), Thr (T) and Tyr (Y) are used to specifically replace hydrophobic residues Leu (L), Ile (I), Val (V) and Phe (F), thus rendering the 7 transmembrane α‐helical segments detergent‐free and water‐soluble following removal from the cell membrane. These GPCR chemokine receptors not only retain their secondary α‐helical structure and overall‐fold, but also retain their ligand‐binding activities . CD played a key role in monitoring the systematic changes and ensuring that the engineered synthetic receptor proteins maintain their structures.…”

Elucidating the Structure of Membrane Proteins

“…They take a membrane protein andapply personalized computer algorithms that result in the production of a code, which is much simpler than previous attempts to make the proteins soluble. This enables the swapping of some hydrophobic amino acids for hydrophilic ones [4]. …”

PSS: An enabling QTY server for designing water-soluble α-helical transmembrane proteins

“…In our recently published study, which used GPCRs as model proteins, a code-based approach, named the QTY method, was successfully developed for solubilizing TM proteins. It is considered a revolutionary new method for making a membrane protein water-soluble (6). The method was tested by making several GPCRs, including CCR5, CXCR4, CCR10 and CXCR7, water-soluble.…”

“…After obtaining the input sequence and TM region information, the server will substitute all changeable residues in the TM regions and output a sequence for the designed protein. By default, QTY code is performed, including the investigations reported in our previous study (6). Currently, we have completed all designs on human GPCRs, including related statistical analyses ( Supplementary File 4).A distribution map containing these 825 human GPCRs and their QTY variants is shown (Fig.…”