title: Apo-calmodulin binds with its C-terminal domain to the N-methyl-D-aspartate receptor NR1 C0 region.
abstract: Calmodulin (CaM) is the major Ca2+ sensor in eukaryotic cells. It consists of four EF-hand Ca2+ binding motifs, two in its N-terminal domain and two in its C-terminal domain. Through a negative feedback loop, CaM inhibits Ca2+ influx through N-methyl-D-aspartate-type glutamate receptors in neurons by binding to the C0 region in the cytosolic tail of the NR1 subunit. Ca2+ -depleted (apo)CaM is pre-associated with a variety of ion channels for fast and effective regulation of channel activities upon Ca2+ influx. Using the NR1 C0 region for fluorescence and circular dichroism spectroscopy studies we found that not only Ca2+ -saturated CaM but also apoCaM bound to NR1 C0. In vitro interaction assays showed that apoCaM also binds specifically to full-length NR1 solubilized from rat brain and to the complete C terminus of the NR1 splice form that contains the C0 plus C2' domain. The Ca2+ -independent interaction of CaM was also observed with the isolated C-but not N-terminal fragment of calmodulin in the independent spectroscopic assays. Fluorescence polarization studies indicated that apoCaM associated via its C-terminal domain with NR1 C0 in an extended conformation and collapsed to adopt a more compact conformation of faster rotational mobility in its complex with NR1 C0 upon addition of Ca2+. Our results indicate that apoCaM is associated with NR1 and that the complex of CaM bound to NR1 C0 undergoes a dramatic conformational change when Ca2+ binds to CaM.
authors.affiliation: Department of Biochemistry, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA 52242-1109, USA.
authors.forename: Zeynep
authors.initials: Z
authors.lastname: Akyol
authors.forename: Jason A
authors.initials: JA
authors.lastname: Bartos
authors.forename: Michelle A
authors.initials: MA
authors.lastname: Merrill
authors.forename: Laurel A
authors.initials: LA
authors.lastname: Faga
authors.forename: Olav R
authors.initials: OR
authors.lastname: Jaren
authors.forename: Madeline A
authors.initials: MA
authors.lastname: Shea
authors.forename: Johannes W
authors.initials: JW
authors.lastname: Hell
mesh_terms: D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000737:chemistry / Q000378:metabolism*; D002942:Circular Dichroism; D005454:Fluorescence Polarization; D016194:Receptors, N-Methyl-D-Aspartate / Q000737:chemistry / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
chemical_list: D002147:Calmodulin; D016194:Receptors, N-Methyl-D-Aspartate; D002118:Calcium