title: Solution NMR structures of the C-domain of Tetrahymena cytoskeletal protein Tcb2 reveal distinct calcium-induced structural rearrangements.
abstract: Tcb2 is a calcium-binding protein that localizes to the membrane-associated skeleton of the ciliated protozoan Tetrahymena thermophila with hypothesized roles in ciliary movement, cell cortex signaling, and pronuclear exchange. Tcb2 has also been implicated in a unique calcium-triggered, ATP-independent type of contractility exhibited by filamentous networks isolated from the Tetrahymena cytoskeleton. To gain insight into Tcb2's structure-function relationship and contractile properties, we determined solution NMR structures of its C-terminal domain in the calcium-free and calcium-bound states. The overall architecture is similar to other calcium-binding proteins, with paired EF-hand calcium-binding motifs. Comparison of the two structures reveals that Tcb2-C's calcium-induced conformational transition differs from the prototypical calcium sensor calmodulin, suggesting that the two proteins play distinct functional roles in Tetrahymena and likely have different mechanisms of target recognition. Future studies of the full-length protein and the identification of Tcb2 cellular targets will help establish the molecular basis of Tcb2 function and its unique contractile properties. Proteins 2016; 84:1748-1756. © 2016 Wiley Periodicals, Inc.
authors.affiliation: Department of Physics and Astronomy, Drake University, Des Moines, Iowa, 50311. adina.kilpatrick@drake.edu.
authors.forename: Adina M
authors.initials: AM
authors.lastname: Kilpatrick
authors.affiliation: Department, of Biology, Drake University, Des Moines, Iowa, 50311.
authors.forename: Jerry E
authors.initials: JE
authors.lastname: Honts
authors.affiliation: Department, of Biology, Drake University, Des Moines, Iowa, 50311.
authors.forename: Heidi M
authors.initials: HM
authors.lastname: Sleister
authors.affiliation: Roy J. and Lucille A. Carver College of Medicine NMR Facility, University of Iowa, Iowa City, Iowa, 52242.
authors.forename: C Andrew
authors.initials: CA
authors.lastname: Fowler
mesh_terms: D000595:Amino Acid Sequence; D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002147:Calmodulin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D003599:Cytoskeleton / Q000737:chemistry / Q000378:metabolism; D020832:EF Hand Motifs; D015870:Gene Expression; D056004:Molecular Dynamics Simulation; D019906:Nuclear Magnetic Resonance, Biomolecular; D000072417:Protein Domains; D017433:Protein Structure, Secondary; D015800:Protozoan Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D016808:Tetrahymena thermophila / Q000235:genetics* / Q000378:metabolism
chemical_list: D002135:Calcium-Binding Proteins; D002147:Calmodulin; D003598:Cytoskeletal Proteins; D015800:Protozoan Proteins; D002118:Calcium
keywords: EF-hand; TCBP-25; calcium signaling; calcium-binding protein; calmodulin; conformational change; cytoskeleton; helical packing; hydrophobic surface; protein structure