title: Calcineurin regulatory subunit B is a unique calcium sensor that regulates calcineurin in both calcium-dependent and calcium-independent manner.
abstract: Calcineurin subunit B (CNB), a regulatory subunit of calcineurin, is a member of EF-hand calcium (Ca(2+))-binding protein superfamily. In this study, we performed phosphatase activity, pull-down, and circular dichroism analyses, which shows Ca(2+)-free CNB (apo-CNB) is able to bind CNA (Calcineurin subunit A) and regulate its phosphatase activity, albeit to a lesser extent than Ca(2+)-saturated CNB (holo-CNB). This is supported by subsequent molecular dynamics (MD) simulations which aimed to examine calcium-induced conformational changes of CNB, using both holo-CNB and apo-CNB. Based on the trajectories of MD, we found that there were no drastic changes between holo-CNB and apo-CNB. The modest differences seen are mainly reflected in the interhelical angles of the four EF-hand motifs and solvent accessible surface area of the hydrophobic groove which is responsible for CNA binding. Interestingly, this hydrophobic groove was largely retained in both holo-CNB and apo-CNB. Comparative analyses show that the calcium-induced conformational change in CNB is remarkably different from that of the two prototypical EF-hand calcium-binding proteins, namely, calmodulin and recoverin. This is the first time that CNB is shown to activate CNA in the absence of Ca(2+).
authors.affiliation: Beijing Key Laboratory, Department of Biochemistry and Molecular Biology, Beijing Normal University, Beijing 100875, People's Republic of China.
authors.forename: Jing
authors.initials: J
authors.lastname: Li
authors.forename: ZhiGuang
authors.initials: Z
authors.lastname: Jia
authors.forename: WenChang
authors.initials: W
authors.lastname: Zhou
authors.forename: Qun
authors.initials: Q
authors.lastname: Wei
mesh_terms: D000818:Animals; D019703:Calcineurin / Q000737:chemistry / Q000502:physiology*; D002118:Calcium / Q000737:chemistry / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000737:chemistry; D002147:Calmodulin / Q000737:chemistry; D004926:Escherichia coli / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D008958:Models, Molecular; D008968:Molecular Conformation; D011485:Protein Binding; D011487:Protein Conformation; D051603:Recoverin / Q000737:chemistry; D012984:Software; D013053:Spectrophotometry / Q000379:methods
chemical_list: D002135:Calcium-Binding Proteins; D002147:Calmodulin; D051603:Recoverin; D019703:Calcineurin; D002118:Calcium