title: Structural and thermodynamic studies of the tobacco calmodulin-like rgs-CaM protein.
abstract: The tobacco calmodulin-like protein rgs-CaM is involved in host defense against virus and is reported to possess an associated RNA silencing suppressor activity. Rgs-CaM is also believed to act as an antiviral factor by interacting and targeting viral silencing suppressors for autophagic degradation. Despite these functional data, calcium interplay in the modulation of rgs-CaM is still poorly understood. Here we show that rgs-CaM displays a prevalent alpha-helical conformation and possesses three functional Ca2+-binding sites. Using computational modeling and molecular dynamics simulation, we demonstrate that Ca2+binding to rgs-CaM triggers expansion of its tertiary structure with reorientation of alpha-helices within the EF-hands. This conformational change leads to the exposure of a large negatively charged region that may be implicated in the electrostatic interactions between rgs-CaM and viral suppressors. Moreover, the kdvalues obtained for Ca2+binding to the three functional sites are not within the affinity range of a typical Ca2+sensor.
authors: Universidade Estadual Paulista (UNESP), Instituto de Biociências, Departamento de Genética, Botucatu, SP, Brazil.
authors: Rodrigo K
authors: RK
authors: Makiyama
authors: Universidade Estadual Paulista (UNESP), Instituto de Biociências, Departamento de Física e Biofísica, Botucatu, SP, Brazil.
authors: Carlos A H
authors: CA
authors: Fernandes
authors: Universidade Estadual Paulista (UNESP), Instituto de Biociências, Departamento de Física e Biofísica, Botucatu, SP, Brazil.
authors: Thiago R
authors: TR
authors: Dreyer
authors: Universidade Estadual Paulista (UNESP), Instituto de Biociências, Departamento de Genética, Botucatu, SP, Brazil.
authors: Bruno S
authors: BS
authors: Moda
authors: Universidade Estadual Paulista (UNESP), Instituto de Biociências, Departamento de Física e Biofísica, Botucatu, SP, Brazil.
authors: Fabio F
authors: FF
authors: Matioli
authors: Universidade Estadual Paulista (UNESP), Instituto de Biociências, Departamento de Física e Biofísica, Botucatu, SP, Brazil.
authors: Marcos R M
authors: MR
authors: Fontes
authors: Universidade Estadual Paulista (UNESP), Instituto de Biociências, Departamento de Genética, Botucatu, SP, Brazil. Electronic address: igmaia@ibb.unesp.br.
authors: Ivan G
authors: IG
authors: Maia
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D003001:Cloning, Molecular; D020832:EF Hand Motifs; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D007700:Kinetics; D056004:Molecular Dynamics Simulation; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D000072417:Protein Domains; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D055672:Static Electricity; D013816:Thermodynamics; D014026:Nicotiana / Q000737:chemistry* / Q000378:metabolism
chemical_list: D010940:Plant Proteins; D011994:Recombinant Proteins; C414615:rgs-CaM protein, Nicotiana tabacum; D002118:Calcium
keywords: Ca(2+)-binding protein; Calmodulin-like protein; rgs-CaM