Abstract
The eukaryotic flagellum/cilium is a prominent organelle with conserved structure and diverse functions. Euglena gracilis, a photosynthetic and highly adaptable protist, employs its flagella for both locomotion and environmental sensing. Using proteomics of isolated E.gracilis flagella we identify nearly 1700 protein groups, which challenges previous estimates of the protein complexity of motile eukaryotic flagella. We not only identified several unexpected similarities shared with mammalian flagella, including an entire glycolytic pathway and proteasome, but also document a vast array of flagella-based signal transduction components that coordinate gravitaxis and phototactic motility. By contrast, the pellicle was found to consist of >900 protein groups, containing additional structural and signalling components. Our data identify significant adaptations within the E.gracilis flagellum, many of which are clearly linked to the highly flexible lifestyle.
Highlights
The flagellum is an important structure present across the tree of life, with roles including motility, signalling and development (Diniz et al, 2012)
We find signal transduction pathways coordinated by the E. gracilis flagella and unusual metabolic features suggesting novel functions
The flagellar fraction was centrifuged at 45 000 g in a 70 Ti rotor (Beckman Coulter) for 30 min at 4°C and flagellar pellets were resuspended in a small volume of 100 mM sodium phosphate buffer (SPB), pH 7.0, centrifuged and resuspended twice more to wash the flagella
Summary
The flagellum is an important structure present across the tree of life, with roles including motility, signalling and development (Diniz et al, 2012). The eukaryotic flagellum or cilium shares a universal axoneme structure, characterized by nine outer microtubule doublets which evolved independently from the prokaryotic flagellum. Capable of beating, possess two central microtubule singlets, tethered by radial spokes to the outer doublets which are absent from nonmotile forms, including primary cilia of metazoan cells. Motile flagella are present in the majority of single-celled eukaryotes or protists for at least part of their life cycles, playing critical roles in movement and environmental sensing (Leander et al, 2017). Nonmotile cilia are present in various cells of multicellular organisms, where they coordinate critical signalling pathways. Cilia defects are associated with a number of human disorders referred to as ciliopathies, which include polycystic kidney disease, infertility, situs invertus and blindness; many of the genes responsible are part of the intraflagellar transport (IFT) system, an ancient component of the protocoatomer system (Waters & Beales, 2011; Rout & Field, 2017)
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