title: Crystal structure of cardiac troponin C regulatory domain in complex with cadmium and deoxycholic acid reveals novel conformation.
abstract: The amino-terminal regulatory domain of cardiac troponin C (cNTnC) plays an important role as the calcium sensor for the troponin complex. Calcium binding to cNTnC results in conformational changes that trigger a cascade of events that lead to cardiac muscle contraction. The cardiac N-terminal domain of TnC consists of two EF-hand calcium binding motifs, one of which is dysfunctional in binding calcium. Nevertheless, the defunct EF-hand still maintains a role in cNTnC function. For its structural analysis by X-ray crystallography, human cNTnC with the wild-type primary sequence was crystallized under a novel crystallization condition. The crystal structure was solved by the single-wavelength anomalous dispersion method and refined to 2.2 Å resolution. The structure displays several novel features. Firstly, both EF-hand motifs coordinate cadmium ions derived from the crystallization milieu. Secondly, the ion coordination in the defunct EF-hand motif accompanies unusual changes in the protein conformation. Thirdly, deoxycholic acid, also derived from the crystallization milieu, is bound in the central hydrophobic cavity. This is reminiscent of the interactions observed for cardiac calcium sensitizer drugs that bind to the same core region and maintain the "open" conformational state of calcium-bound cNTnC. The cadmium ion coordination in the defunct EF-hand indicates that this vestigial calcium binding site retains the structural and functional elements that allow it to coordinate a cadmium ion. However, it is a result of, or concomitant with, large and unusual structural changes in cNTnC.
authors.affiliation: Department of Molecular Biology and Biochemistry, Simon Fraser University, South Science Building, 8888 University Drive, Burnaby, British Columbia, Canada, V5A 1S6.|Department of Biomedical Physiology and Kinesiology, Molecular Cardiac Physiology Group, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, Canada, V5A 1S6.
authors.forename: Alison Yueh
authors.initials: AY
authors.lastname: Li
authors.affiliation: Department of Molecular Biology and Biochemistry, Simon Fraser University, South Science Building, 8888 University Drive, Burnaby, British Columbia, Canada, V5A 1S6.
authors.forename: Jaeyong
authors.initials: J
authors.lastname: Lee
authors.affiliation: Department of Biochemistry, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA.
authors.forename: Dominika
authors.initials: D
authors.lastname: Borek
authors.affiliation: Department of Biochemistry, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA.
authors.forename: Zbyszek
authors.initials: Z
authors.lastname: Otwinowski
authors.affiliation: Department of Biomedical Physiology and Kinesiology, Molecular Cardiac Physiology Group, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, Canada, V5A 1S6.|Cardiovascular Sciences, Child and Family Research Institute, 950 West 28 Ave, Vancouver, BC, Canada V5Z 4H4.|Department of Molecular Biology and Biochemistry, Simon Fraser University, South Science Building, 8888 University Drive, Burnaby, British Columbia, Canada, V5A 1S6.
authors.forename: Glen F
authors.initials: GF
authors.lastname: Tibbits
authors.affiliation: Department of Molecular Biology and Biochemistry, Simon Fraser University, South Science Building, 8888 University Drive, Burnaby, British Columbia, Canada, V5A 1S6.|Department of Biomedical Physiology and Kinesiology, Molecular Cardiac Physiology Group, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, Canada, V5A 1S6.
authors.forename: Mark
authors.initials: M
authors.lastname: Paetzel
mesh_terms: D001665:Binding Sites; D002104:Cadmium / Q000378:metabolism*; D018360:Crystallography, X-Ray; D003840:Deoxycholic Acid / Q000378:metabolism*; D020832:EF Hand Motifs; D006321:Heart / Q000502:physiology*; D006801:Humans; D008958:Models, Molecular; D008968:Molecular Conformation; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D011487:Protein Conformation; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D019209:Troponin C / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D019209:Troponin C; D003840:Deoxycholic Acid; D002104:Cadmium