The insect mXR metabotropic glutamate-like receptors (mXR) diverge from classical metabotropic glutamate receptors as they lack the residues that interact with the the gamma-carboxylic group of glutamate. The ligand for mtt has not been identified, but experiments with head extracts indicate an endogenous ligand with a primary amino group and it may be involved in the avoidance response to L-canavanine. (Adapted from FBrf0174795 and FBrf0221506.)