Two mGluR7-derived peptides corresponding to residues 856 to 879 and 856 to 875 are known to bind to Ca2+-saturated calmodulin (Ca2+/CaM), and their binding manners are thought to differ. Met872 function is believed as one of the anchor residues for CaM-binding only in the shorter peptide. To uncover the role of Met872 in CaM-binding, we prepared a mutant of the long peptide, mGluR7 (M872A), in which Met872 was replaced with Ala. We used the mutant together with the two peptides to perform NMR-titration experiments to monitor interaction with stable isotope-labeled CaM. Interaction of Ca2+/CaM with mGluR7 (M872A) caused a spectrum that differed from that of Ca2+/CaM with the long peptide, suggesting that Met872 of mGluR7 could be involved in CaM-binding even in the long peptide. Analyses of all NMR data suggested that the binding between Ca2+/CaM and mGluR7 occurs in some conformational equilibrium manner. The unique CaM-binding properties caused by Met872 may be related to mGluR7's function. (C) 2019 Elsevier Inc. All rights reserved.