Unusual characteristics of ciliate actins

Abstract

Actin is a cytoskeletal protein that is ubiquitous in eukaryotes, hence the corresponding genes and proteins have been isolated from numerous organisms as dierent as animals, plants, fungi and protozoa. Several atomic models are available for the monomeric as well as the ®lamentous form, and more than 70 proteins that bind actin and control ®lament dynamics have been isolated from diverse eukaryotes. Moreover, the function and dynamics of the actin cytoskeleton in several eukaryotic systems have been depicted in depth. Unlike other protozoa, such as amoeba, actin is not an abundant protein in ciliates, whose cytoskeleton is mainly composed of microtubular arrays. Ciliate actin has been studied in several species, and it was established early on that this ciliate protein is very dierent from that of other eukaryotes. Similarly, the actin-binding proteins studied in ciliates display great dierences with those of other eukaryotes. Consequently, ciliate actin has been considered as``unconventional,'' and this review focuses on molecular data leading to this conclusion.

Transcriptomic Differences between Free-Living and Parasitic Chilodonella uncinata (Alveolata, Ciliophora)

“…In this study, compared with the free-living C. uncinata, the parasitic C. uncinata had a higher expression of actin and dynein heavy chain. Actin is a cytoskeletal protein which is ubiquitous in eukaryotes [52], and required for normal ciliary motility and phagocytosis [53]. In the model ciliates Tetrahymena and Paramecium, actin was detected at the oral apparatus [54,55], food vacuoles [56], cytoproct [57], basal bodies [54,55], and cilia [51,54,58].…”

Highly Divergent Actins from Karyorelictean, Heterotrich, and Litostome Ciliates1

“…Ciliate actins showed that they are indeed remote from the actins of skeletal muscle. Identities of the less conserved subdomain 2, subdomain 4, and the region of amino acids 270–337 of subdomain 3 in the actins of these five ciliates are as low as the actins of T. pyriformis, P. tetraurelia and H. caviola to those of the conventional actins (Villalobo et al 2001). These differences in amino acid sequences of ciliate actins are resulted in long branch lengths in the phylogenetic tree.…”

Emerging Functions of Actins and Actin Binding Proteins in Trypanosomatids

“…The main features that define conventional (or canonical) actins are based on their following properties: (1) they form long and stable filaments having width between 7 and 10 nm in the presence of a divalent cation as Mg +2 , with or without ATP; (2) they bind DNase I and inhibit its activity; (3) their filaments are stabilized by phallotoxins and destabilized by cytochalasins or latrunculins ( Reisler, 1993 ; Wakatsuki et al, 2001 ); and (4) their filament dynamics is regulated by a set of about 20 core ABPs that include actin depolymerizing factor (ADF)/cofilins, twinfilin, profilin, gelsolin, CAP/Srv2, formin, Arp2/3 complex, β-thymosin, troponin, filamin, fimbrin, villin, actinin, plastin, spectrin and CapZ. However, lower eukaryotic organisms such as Plasmodium , Toxoplasma , Trypanosoma , Leishmania , Giardia , Amoebae and Ciliate group of protozoans contain actins which display highly unusual characteristics ( Villalobo et al, 2001 ; Gupta et al, 2015 ). While some of these organisms express actins and ABPs that exhibit unusual biochemical and functional characteristics, there are others, such as Giardia lamblia , which express single copy of highly divergent actin ( Drouin et al, 1995 ), and their genome lacks genes that encode the core ABPs, which are essentially required to regulate actin dynamics in higher eukaryotic organisms ( Morrison et al, 2007 ; Pollard, 2016 ).…”