title: Backbone and side-chain chemical shift assignments for the C-terminal domain of Tcb2, a cytoskeletal calcium-binding protein from Tetrahymena thermophila.
abstract: Tcb2 is a putative calcium-binding protein from the membrane-associated cytoskeleton of the ciliated protozoan Tetrahymena thermophila. It has been hypothesized to participate in several calcium-mediated processes in Tetrahymena, including ciliary movement, cell cortex signaling, and pronuclear exchange. Sequence analysis suggests that the protein belongs to the calmodulin family, with N- and C-terminal domains connected by a central linker, and two helix-loop-helix motifs in each domain. However, its calcium-binding properties, structure and precise biological function remain unknown. Interestingly, Tcb2 is a major component of unique contractile fibers isolated from the Tetrahymena cytoskeleton; in these fibers, addition of calcium triggers an ATP-independent type of contraction. Here we report the (1)H, (13)C and (15)N backbone and side-chain chemical shift assignments of the C-terminal domain of the protein (Tcb2-C) in the absence and presence of calcium ions. (1)H-(15)N HSQC spectra show that the domain is well folded both in the absence and presence of calcium, and undergoes a dramatic conformational change upon calcium addition. Secondary structure prediction from chemical shifts reveals an architecture encountered in other calcium-binding proteins, with paired EF-hand motifs connected by a flexible linker. These studies represent a starting point for the determination of the high-resolution solution structure of Tcb2-C at both low and high calcium levels, and, together with additional structural studies on the full-length protein, will help establish the molecular basis of Tcb2 function and unique contractile properties.
authors.affiliation: Department of Physics and Astronomy, Drake University, 2507 University Avenue, Harvey Ingham Hall of Science, Room 24, Des Moines, IA, 50311-4516, USA. adina.kilpatrick@drake.edu.
authors.forename: Adina M
authors.identifier: 0000-0001-7947-4951
authors.initials: AM
authors.lastname: Kilpatrick
authors.affiliation: Department of Biology, Drake University, Des Moines, IA, 50311-4516, USA.
authors.forename: Theodore E
authors.initials: TE
authors.lastname: Gurrola
authors.affiliation: Department of Biology, Drake University, Des Moines, IA, 50311-4516, USA.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Sterner
authors.affiliation: Department of Biology, Drake University, Des Moines, IA, 50311-4516, USA.
authors.forename: Heidi M
authors.initials: HM
authors.lastname: Sleister
authors.affiliation: Department of Biology, Drake University, Des Moines, IA, 50311-4516, USA.
authors.forename: Jerry E
authors.initials: JE
authors.lastname: Honts
authors.affiliation: University of Iowa Roy J. and Lucille A. Carver College of Medicine NMR Facility, Iowa City, IA, 52242-1109, USA.
authors.forename: C Andrew
authors.initials: CA
authors.lastname: Fowler
mesh_terms: D000595:Amino Acid Sequence; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism*; D019906:Nuclear Magnetic Resonance, Biomolecular; D000072417:Protein Domains; D015800:Protozoan Proteins / Q000737:chemistry* / Q000378:metabolism*; D016808:Tetrahymena thermophila / Q000166:cytology*
chemical_list: D002135:Calcium-Binding Proteins; D015800:Protozoan Proteins
keywords: Calcium-binding protein; Contractility; Cytoskeletal; TCBP-25; Tcb2; Tetrahymena thermophila