title: Structural studies of the Ca(2+) regulatory domain of Drosophila Na(+)/Ca (2+) exchanger CALX.
abstract: CALX, the NCX homolog in Drosophila, involves in light-mediated Ca(2+) homeostasis in sensory neuronal cells. CALX exhibits a unique negative Ca(2+) regulatory property mediated by Ca2+ binding at its intracellular regulatory domain. Our structural studies of individual CBD1 or CBD2 domain reveal that CBD1 is the only Ca(2+) binding domain in CALX. Crystal structures of the entire Ca(2+) regulatory domain CBD12 from two alternative splicing isoforms, CALX1.1 and CALX1.2, demonstrate that CBD1 and CBD2 form an open V-shaped conformation with four Ca(2+) ions bound on the CBD domain interface. The structures together with Ca(2+) binding analyses strongly argue that the Ca(2+) inhibition of CALX is achieved by interdomain conformational change induced by Ca(2+) binding at CBD1. The conformational difference between the two isoforms also raises a hypothesis that alternative splicing residues adjust the interdomain orientation angle between CBD1 and CBD2 to modify the Ca(2+) regulatory property of the exchanger. These studies not only establish structural basis to understand the inhibitory Ca(2+) regulation and the alternative splicing modification of CALX, but also shed light on the general Ca(2+) regulatory mechanism of other mammalian NCX proteins.
authors.affiliation: Department of Biochemistry and Molecular Biology, The University of Texas Houston Medical School, Houston, TX 77030, USA. lei.zheng@uth.tmc.edu
authors.forename: Lei
authors.initials: L
authors.lastname: Zheng
authors.forename: Mousheng
authors.initials: M
authors.lastname: Wu
authors.forename: Shuilong
authors.initials: S
authors.lastname: Tong
mesh_terms: D017398:Alternative Splicing / Q000502:physiology*; D000818:Animals; D017920:Antiporters / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D002412:Cations; D029721:Drosophila Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster; D017136:Ion Transport / Q000502:physiology; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D019831:Sodium-Calcium Exchanger / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D017920:Antiporters; C108396:Calx protein, Drosophila; D002412:Cations; D029721:Drosophila Proteins; D020033:Protein Isoforms; D019831:Sodium-Calcium Exchanger; D002118:Calcium