title: Molecular evolution of troponin I and a role of its N-terminal extension in nematode locomotion.
abstract: The troponin complex, composed of troponin T (TnT), troponin I (TnI), and troponin C (TnC), is the major calcium-dependent regulator of muscle contraction, which is present widely in both vertebrates and invertebrates. Little is known about evolutionary aspects of troponin in the animal kingdom. Using a combination of data mining and functional analysis of TnI, we report evidence that an N-terminal extension of TnI is present in most of bilaterian animals as a functionally important domain. Troponin components have been reported in species in most of representative bilaterian phyla. Comparison of TnI sequences shows that the core domains are conserved in all examined TnIs, and that N- and C-terminal extensions are variable among isoforms and species. In particular, N-terminal extensions are present in all protostome TnIs and chordate cardiac TnIs but lost in a subset of chordate TnIs including vertebrate skeletal-muscle isoforms. Transgenic rescue experiments in Caenorhabditis elegans striated muscle show that the N-terminal extension of TnI (UNC-27) is required for coordinated worm locomotion but not in sarcomere assembly and single muscle-contractility kinetics. These results suggest that N-terminal extensions of TnIs are retained from a TnI ancestor as a functional domain.
authors: Department of Pathology and Department of Cell Biology, Emory University, Atlanta, Georgia.
authors: Dawn E
authors: DE
authors: Barnes
authors: School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia.|School of Engineering and Sciences, Technológico de Monterrey, Monterrey, Nuevo León, Mexico.
authors: Hyundoo
authors: H
authors: Hwang
authors: Department of Pathology and Department of Cell Biology, Emory University, Atlanta, Georgia.
authors: Kanako
authors: K
authors: Ono
authors: School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia.|Interdisciplinary Program of Bioengineering, Georgia Institute of Technology, Atlanta, Georgia.|The Petit Institute for Bioengineering and Biosciences, Georgia Institute of Technology, Atlanta, Georgia.
authors: Hang
authors: H
authors: Lu
authors: Department of Pathology and Department of Cell Biology, Emory University, Atlanta, Georgia.
authors: Shoichiro
authors: S
authors: Ono
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics / Q000378:metabolism; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism; D019143:Evolution, Molecular; D008124:Locomotion / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D012518:Sarcomeres / Q000235:genetics / Q000378:metabolism; D019210:Troponin I / Q000235:genetics / Q000378:metabolism
chemical_list: D029742:Caenorhabditis elegans Proteins; D019210:Troponin I
keywords: actin; contraction; muscle; myosin; troponin