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.

Centrin in the groove: immunolocalisation of centrin and microtubules in the putatively primitive protistChilomastix cuspidata (Retortamonadida)

“…Centrin plays a variety of roles including contraction, calcium signalling, and in the positioning of organelles and has been observed in a variety of protists (e.g., Allen et al 1998;Amos et al 1975;David and Vigues 1994;Garreau de Loubresse et al 1991;Harper et al 1995;Huang et al 1988;Levy et al 1996;Melkonian et al 1992;Piperno et al 1992;Salisbury et al 1984Salisbury et al , 1987Salisbury et al , 1988Salisbury 1989, 1994;Taillon et al 1992;Wright et al 1985Wright et al ,1989, plants (Del Vecchio et al 1997, Vaughn and Harper 1998, Vaughn et al 1993, and animals (Baron et al 1994, Paoletti et al 1996, Schiebel and Bornens 1995.…”

Functional diversification of centrins and cell morphological complexity

“…Remarkably, in acentriolar organisms, which form basal bodies only at a specific stage of their life cycle, such as in Naegleria or Marsilea, centrin synthesis strictly correlates with assembly of basal bodies (Klink and Wolniak, 2001;Levy et al, 1996). Centrin is a major constituent of the diverse arrays of MTOC-associated contractile fibres present in unicellular organisms and it mediates Ca 2+ -induced contractility as shown for the basal-body-associated fibres in Chlamydomonas (Hayashi et al, 1998;Salisbury et al, 1987), the spasmonemes in Vorticella (Amos et al, 1975;Maciejewski et al, 1999), the myonemes in Eudiplodinium (David and Vigues, 1994) and the infraciliary lattice (ICL) in Paramecium (Garreau de Loubresse et al, 1991). The discovery in yeast of Sfi1p, a large protein able to bind centrin at many sites (Kilmartin, 2003), has provided a molecular model to account for centrin function in Ca…”

Characterization of Centrin Genes in Paramecium

“…These filamentous arrays are varied in their morphology and function, as exemplified by the striated rootlets and nucleus-basal body connectors of unicellular algae (Salisbury et al, 1984(Salisbury et al, , 1988Schulze et al, 1987;Taillon et al, 1992;Katsaros et al, 1993 ;Sanders and Salisbury, 1994), or the myonemes of the ciliate Eudiplodinum maggii (David and Viguks, 1994).…”