Epiplasts: Membrane Skeletons and Epiplastin Proteins in Euglenids, Glaucophytes, Cryptophytes, Ciliates, Dinoflagellates, and Apicomplexans

Abstract

Membrane skeletons associate with the inner surface of the plasma membrane to provide support for the fragile lipid bilayer and an elastic framework for the cell itself. Several radiations, including animals, organize such skeletons using actin/spectrin proteins, but four major radiations of eukaryotic unicellular organisms, including disease-causing parasites such as Plasmodium, have been known to construct an alternative and essential skeleton (the epiplast) using a class of proteins that we term epiplastins. We have identified epiplastins in two additional radiations and present images of their epiplasts using electron microscopy. We analyze the sequences and secondary structure of 219 epiplastins and present an in-depth overview and analysis of their known and posited roles in cellular organization and parasite infection. An understanding of epiplast assembly may suggest therapeutic approaches to combat infectious agents such as Plasmodium as well as approaches to the engineering of useful viscoelastic biofilms.

Fussing About Fission: Defining Variety Among Mainstream and Exotic Apicomplexan Cell Division Modes

“…From the outside in, it is built up from three uniformly conserved elements: alveolar vesicles (alveoli) that anchor the myosin motor enabling motility (Frenal et al, 2017a), an epiplastin (a.k.a. alveolar) protein meshwork (Goodenough et al, 2018), and a series of sub-pellicular, longitudinal microtubules emanating from the apical end. The number and length of the microtubules vary across parasite species and stage (Spreng et al, 2019), but the alveoli and epiplastin meshwork are universally conserved and make up the inner membrane complex (IMC) (Kono et al, 2012).…”

Sequence and Properties of Cagein, a Coiled‐Coil Scaffold Protein Linking Basal Bodies in the Polykinetids of the Ciliate Euplotesaediculatus

“…Goodenough et al. (2018) and Preisner et al. (2018) provide extensive catalogs and discussion of these manifold cytoskeletal proteins in recent reviews.…”

“…These strategies typically invoke arrangements of multiple cytoskeletal proteins (and sometimes membranes) to allow flexibility and resilience, while protecting against varied environmental insults and challenges. Goodenough et al (2018) and Preisner et al (2018) provide extensive catalogs and discussion of these manifold cytoskeletal proteins in recent reviews. Among protist models, ciliates have been especially well studied.…”

The Modular Circuitry of Apicomplexan Cell Division Plasticity

“…Palmitoylation of IMC proteins anchors them into the alveolar vesicles, which is an essential step across species and division modes (Dogga and Frenal, 2020;Wang et al, 2020b). There is a wide variety of proteins localizing to the IMC, but proteins with an alveolin repeat are intermediate filament-like and assemble in a meshwork of proteins undergirding the alveolar vesicles (Gould et al, 2008;Anderson-White et al, 2011;Kono et al, 2012;Tremp et al, 2014;Chen et al, 2015a;Goodenough et al, 2018). The IMC soluble proteins (ISP), which do not become crosslinked in the meshwork, are critical in both T. gondii tachyzoite and Plasmodium ookinete formation (Beck et al, 2010;Fung et al, 2012;Wang et al, 2020b).…”