GCGR and type 2 diabetes mellitus: Peptides are sustainable alternatives to conventionaltherapeuticsfor G protein-coupled receptor (GPCR) linked disorders, promisingbiocompatible and tailorable next-generation therapeutics for metabolicdisorders including type-2 diabetes, as agonists of the glucagon receptor(GCGR) and the glucagon-like peptide-1 receptor (GLP-1R).