title: Competitive binding of calmodulin isoforms to calmodulin-binding proteins: implication for the function of calmodulin isoforms in plants.
abstract: In plants, multiple calmodulin (CaM) isoforms exist in an organism which vary in their primary structures in as much as 32 residues out of their 148 amino acids. These CaM isoforms show differences in their expression patterns and/or target enzyme activation ability. To further understand the biological significance of CaM isoforms, we examined whether CaM isoforms act on specific regulatory targets. In gel overlay assays on various soybean tissue extracts, surprisingly, two soybean CaM isoforms (SCaM-1 and SCaM-4) did not show significant differences in their target binding protein profiles, although they exhibited minor differences in their relative target binding affinities. In addition, both SCaM isoforms not only effectively bound five known plant CaMBPs, but also showed competitive binding to these proteins. Finally, immunolocalization experiments with the SCaM proteins in sections of various tissues using specific antibodies revealed similar distribution patterns for the SCaM isoforms except for root tissues, which indicates that the SCaM isoforms are concomitantly expressed in most plant tissues. These results suggest that CaM isoforms may compete for binding to CaMBPs in vivo. This competitive nature of CaM isoforms may allow modulation of Ca(2+)/CaM signaling pathways by virtue of relative abundance and differential target activation potency.
authors.affiliation: Department of Biochemistry, Plant Molecular Biology and Biotechnology Research Center, Gyeongsang National University, Chinju 660-701, South Korea.
authors.forename: S H
authors.initials: SH
authors.lastname: Lee
authors.forename: M C
authors.initials: MC
authors.lastname: Kim
authors.forename: W D
authors.initials: WD
authors.lastname: Heo
authors.forename: J C
authors.initials: JC
authors.lastname: Kim
authors.forename: W S
authors.initials: WS
authors.lastname: Chung
authors.forename: C Y
authors.initials: CY
authors.lastname: Park
authors.forename: H C
authors.initials: HC
authors.lastname: Park
authors.forename: Y H
authors.initials: YH
authors.lastname: Cheong
authors.forename: C Y
authors.initials: CY
authors.lastname: Kim
authors.forename: K J
authors.initials: KJ
authors.lastname: Lee
authors.forename: J D
authors.initials: JD
authors.lastname: Bahk
authors.forename: S Y
authors.initials: SY
authors.lastname: Lee
authors.forename: M J
authors.initials: MJ
authors.lastname: Cho
mesh_terms: D001667:Binding, Competitive; D002135:Calcium-Binding Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D010944:Plants / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D015398:Signal Transduction; D013025:Glycine max / Q000737:chemistry / Q000378:metabolism
chemical_list: D002135:Calcium-Binding Proteins; D002147:Calmodulin; D008565:Membrane Proteins; D020033:Protein Isoforms