title: Calmyonemin: a 23 kDa analogue of algal centrin occurring in contractile myonemes of Eudiplodinium maggii (ciliate).
abstract: Myonemes are bundles of thin filaments (3-6 nm in diameter) which mediate calcium-induced contraction of the whole or only parts of the cell body in a number of protists. In Eudiplodinium maggii, a rumen ciliate which lacks a uniform ciliation of the cell body, myonemes converge toward the bases of apical ciliary zones that can be retracted under stress conditions, entailing immobilization of the cell. An mAB (A69) has been produced that identifies a calcium-binding protein by immunoblot, immunoprecipitation experiments and specifically labels the myonemes in immunoelectron microscopy. Solubility properties, apparent molecular weight (23 kDa) and isoelectric point (4.9) of the myonemal protein, are similar to the values reported for the calcium-modulated contractile protein centrin. Western-blot analysis indicates that the 23 kDa protein cross-reacts antigenically with anti-centrin antibodies. In addition, the 23 kDa protein displays calcium-induced changes in both electrophoretic and chromatographic behaviour, and contains calcium-binding domains that conform to the EF-hand structure, as known for centrin. Based on these observations, we conclude that a calcium-binding protein with major similarities to centrin occurs in the myonemes of E. maggii. We postulate that this protein plays an essential role in myoneme-mediated retraction of the ciliature.
authors.affiliation: URA CNRS 138, Laboratoire de Biologie Comparée des Protistes, Université Blaise Pascal, Aubière, France.
authors.forename: C
authors.initials: C
authors.lastname: David
authors.forename: B
authors.initials: B
authors.lastname: Viguès
mesh_terms: D008841:Actin Cytoskeleton / Q000737:chemistry* / Q000648:ultrastructure; D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal; D000918:Antibody Specificity; D002135:Calcium-Binding Proteins / Q000032:analysis* / Q000737:chemistry / Q000276:immunology; D002868:Chromosomal Proteins, Non-Histone; D002923:Cilia / Q000737:chemistry / Q000648:ultrastructure; D016798:Ciliophora / Q000502:physiology* / Q000648:ultrastructure; D003285:Contractile Proteins / Q000032:analysis* / Q000737:chemistry / Q000276:immunology; D003429:Cross Reactions; D007526:Isoelectric Point; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011233:Precipitin Tests; D017421:Sequence Analysis; D017386:Sequence Homology, Amino Acid
chemical_list: D000911:Antibodies, Monoclonal; D002135:Calcium-Binding Proteins; D002868:Chromosomal Proteins, Non-Histone; D003285:Contractile Proteins; C086964:calmyonemin; C056608:caltractin