Development of a cysteine-deprived and C-terminally truncated GLP-1 receptor

• Seven cysteines are functionally redundant in the GLP-1 receptor.
• Cysteines 174, 226, 296 and 403 are important for the GLP-1-mediated response.
• Leucine 422 marks the limit for C-terminal truncation of the GLP-1 receptor.
• Seven cysteines and 37 C-terminal residues can be removed simultaneously.

The glucagon-like peptide-1 receptor (GLP-1R) belongs to family B of the G-protein coupled receptors (GPCRs), and has become a promising target for the treatment of type 2 diabetes. Here we describe the development and characterization of a fully functional cysteine-deprived and C-terminally truncated GLP-1R. Single cysteines were initially substituted with alanine, and functionally redundant cysteines were subsequently changed simultaneously. Our results indicate that Cys174, Cys226, Cys296 and Cys403 are important for the GLP-1-mediated response, whereas Cys236, Cys329, Cys341, Cys347, Cys438, Cys458 and Cys462 are not. Extensive deletions were made in the C-terminal tail of GLP-1R in order to determine the limit for truncation. As for other family B GPCRs, we observed a direct correlation between the length of the C-terminal tail and specific binding of 125I-GLP-1, indicating that the membrane proximal part of the C-terminal is involved in receptor expression at the cell surface. The results show that seven cysteines and more than half of the C-terminal tail can be removed from GLP-1R without compromising GLP-1 binding or function.