PMID: 24189067

Authors:

Mukund S, Shang Y, Clarke HJ, Madjidi A, Corn JE, Kates L, Kolumam G, Chiang V, Luis E, Murray J, Zhang Y, Hotzel I, Koth CM, Allan BB

Title:

Inhibitory mechanism of an allosteric antibody targeting the glucagon receptor.

Journal:

J Biol Chem. 2013 Nov 4.

Abstract:

Elevated glucagon levels and increased hepatic glucagon receptor (GCGR) signaling contribute to hyperglycemia in type 2 diabetes. We have identified a monoclonal antibody that inhibits GCGR, a class-B G-protein coupled receptor (GPCR), through a unique allosteric mechanism. Binding of this antibody to two distinct sites that lie outside the glucagon binding cleft mediate receptor inhibition. One site consists of a patch of residues that are surface exposed on the face of the extracellular domain (ECD) opposite the ligand-binding cleft while the second binding site consists of residues in the alphaA helix of the ECD. A docking model suggests that the antibody does not occlude the ligand-binding cleft. We solved the crystal structure of GCGR ECD containing a naturally occurring G40S mutation and found a shift in the register of the alphaA helix that prevents antibody binding. We also found that alterations in the alphaA helix impact the normal function of GCGR. We present a model for the allosteric inhibition of GCGR by a monoclonal antibody that may form the basis for the development of allosteric modulators for the treatment of diabetes and other class-B GPCR-related diseases.