The multiple functions of actin in apicomplexan parasites

Abstract

The cytoskeletal protein actin is highly abundant and conserved in eukaryotic cells. It occurs in two different states-the globular (G-actin) form, which can polymerise into the filamentous (F-actin) form, fulfilling various critical functions including cytokinesis, cargo trafficking and cellular motility. In higher eukaryotes, there are several actin isoforms with nearly identical amino acid sequences. Despite the high level of amino acid identity, they display regulated expression patterns and unique non-redundant roles. The number of actin isoforms together with conserved sequences may reflect the selective pressure exerted by scores of actin binding proteins (ABPs) in higher eukaryotes. In contrast, in many protozoans such as apicomplexan parasites which possess only a few ABPs, the regulatory control of actin and its multiple functions are still obscure. Here, we provide a summary of the regulation and biological functions of actin in higher eukaryotes and compare it with the current knowledge in apicomplexans. We discuss future experiments that will help us understand the multiple, critical roles of this fascinating system in apicomplexans. | ACTIN IN MOST EUKARYOTESActin is one of the most abundant proteins in eukaryotic cells and owing to its ability to polymerise into filaments (F-Actin) forming static or highly dynamic networks, plays an important function in many crucial cellular processes. The regulated dynamics of F-actin and crosslinking of individual filaments requires the integration of actin binding proteins (ABPs) with signalling cascades that ultimately regulate actin filament length, stability and anchorage (Hansen & Kwiatkowski, 2013). This control can be achieved at multiple levels, from direct binding of ABPs to post-translational modifications of actin and are based on influencing the basic polymerisation mechanism of this molecule (Dominguez & Holmes, 2011).The atomic structure of monomeric G-actin was first described in 1990. With a molecular weight of 42 kDa (Pollard, 2016

Phosphoproteomic Comparison of Four Eimeria tenella Life Cycle Stages

“…In T. gondii, this protein is a crucial motor for centrosome positioning and apicoplast inheritance [33]. Actin, which has been identified in all apicomplexans [34], was also identified in our results. Actin is crucial for segregation of the apicoplast and parasite maturation in T. gondii and P. falciparum [35,36].…”

“…Additionally, actin is required for fusion of endocytic vesicles and vesicular transport in P. falciparum [38]. Furthermore, actin polymerizes into filaments (F-actin) to form static or highly dynamic networks [34]. In the present study, DEPPs in the SO7h vs. USO and S vs.…”

“…SO comparisons were linked to actin cytoskeleton organization and actin filament bundle organization. Both actin and F-actin play important roles in the E. tenella life cycle, including invasion, gliding motility, egress, vesicular transport, apicoplast inheritance, intracellular replication, actin network maintenance, and material exchange between parasites [34].…”

Disc and Actin-Associated Protein 1 Influence Attachment in the Intestinal Parasite Giardia lamblia

“…For instance, one of Toxoplasma gondii's formins localize exclusively to the conoid [42], a latticelike microtubule organelle which initiates host invasion [43]. Triggered by release of calcium ions, actin polymerization, in coordination with myosins A and H, contributes to conoid extrusion to initiate host invasion [44][45][46]. GlActin polymerization could have an analogous role in controlling the movement of the ventral disc to facilitate attachment.…”

“…For instance, one of Toxoplasma gondii's formins localize exclusively to the conoid [44], a latticelike organelle composed of tubulin which initiates host invasion [45]. There is evidence of coordination between the microtubules of Toxoplasma's glideosome, which is used for actinbased motility, during host invasion [46]. Furthermore, actin polymerization is believed to contribute to conoid extrusion [47,48], and the conoid-localized Myosin H is essential for entry and exit from host cells [49,50].…”