GCGR and type 2 diabetes mellitus: Through 2 μs MD simulations on the apo glucagon receptor (GCGR) and glucagon-bound GCGR performed using GROMACS4.6.1 package [50], we recently discovered that full-length GCGR, a potential drug target for type 2 diabetes [51], has two conformations: an open conformation stabilized by the peptide glucagon and a closed conformation in apo-GCGR, in which the extracellular domain (ECD) forms extensive contacts with the seven transmembrane (7TM) domain (Fig. 4A).