title: Global dynamic conformational changes in the suppressor domain of IP3 receptor by stepwise binding of the two lobes of calmodulin.
abstract: The roles of calmodulin (CaM) have been key points of controversy in the regulation of inositol-1,4,5-trisphosphate receptor (IP(3)R). To address the issue, we studied the interaction between CaM and the suppressor domain of IP(3)R, a key allosteric regulatory domain. First, by means of a pulldown and a fluorescence titration experiment, we confirmed the interaction. Through subsequent NMR binding experiments, we observed dramatic peak disappearances of the suppressor domain on interaction with apo-CaM. The data indicated that apo-CaM induces large-scale dynamic conformational changes in the suppressor domain, involving partial unfolding and subdomain rearrangement. Analysis of the NMR data of CaM surprisingly revealed that its C lobe alone can cause such changes. Further binding experiments showed that calcium allows the free N lobe to bind to the suppressor domain, which induces extra conformational changes in both of the proteins. These results were also confirmed with CaM deletion mutants with either the N or C lobe. On the basis of this novel binding mechanism, we propose a model in which the partial unfolding of the suppressor domain by apo-CaM and the stepwise binding of the N lobe of CaM to the suppressor domain are important elements of calcium/CaM inhibition of IP(3)R. We believe that our working model encompasses previous regulation mechanisms of IP(3)R by calcium/CaM and provides new insights into the CaM-target interaction.
authors.affiliation: Department of Biochemistry and Center for Advanced Medical Education by BK21 Project, School of Medicine, Inha University, Chungsuk Bldg., Rm. 505, Shinheung-dong, Chung-gu, Incheon, Korea, 400-712.
authors.forename: Sunmi
authors.initials: S
authors.lastname: Kang
authors.forename: Hyuknam
authors.initials: H
authors.lastname: Kwon
authors.forename: He
authors.initials: H
authors.lastname: Wen
authors.forename: Youngmin
authors.initials: Y
authors.lastname: Song
authors.forename: Dominique
authors.initials: D
authors.lastname: Frueh
authors.forename: Hee-Chul
authors.initials: HC
authors.lastname: Ahn
authors.forename: Seung Hyun
authors.initials: SH
authors.lastname: Yoo
authors.forename: Gerhard
authors.initials: G
authors.lastname: Wagner
authors.forename: Sunghyouk
authors.initials: S
authors.lastname: Park
mesh_terms: D000494:Allosteric Regulation; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism*; D002417:Cattle; D002942:Circular Dichroism; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008956:Models, Chemical; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D011485:Protein Binding / Q000502:physiology; D017434:Protein Structure, Tertiary
chemical_list: D002147:Calmodulin; D053496:Inositol 1,4,5-Trisphosphate Receptors; D002118:Calcium