Trafficking activity of myosin XXI is required in assembly ofLeishmaniaflagellum

Abstract

SummaryActin-based myosin motors have a pivotal role in intracellular trafficking in eukaryotic cells. The parasitic protozoan organism Leishmania expresses a novel class of myosin, myosin XXI (Myo21), which is preferentially localized at the proximal region of the flagellum. However, its function in this organism remains largely unknown. Here, we show that Myo21 interacts with actin, and its expression is dependent of the growth stage. We further reveal that depletion of Myo21 levels results in impairment of the flagellar assembly and intracellular trafficking. These defects are, however, reversed by episomal complementation. Additionally, it is shown that deletion of the Myo21 gene leads to generation of ploidy, suggesting an essential role of Myo21 in survival of Leishmania cells. Together, these results indicate that actin-dependent trafficking activity of Myo21 is essentially required during assembly of the Leishmania flagellum.

Calmodulin regulates dimerization, motility, and lipid binding of Leishmania myosin XXI

“…6A, we speculate that the monomeric, motile, and lipid-binding conformation corresponds to a myosin-XXI fraction that has been localized at the base of the Leishmania flagellum (3,7). In contrast, the free, cytosolic dimeric fraction of myosin XXI might correspond to the detergent-labile component that has been localized within the flagellum where it could contribute to the structural organization of the actin network (3,7). Apart from demonstrating the presence of actin filaments in the main cell body and the flagellum using immuno-labeling of fixed Leishmania parasites, to date little is known about the structure and dynamics of the actin cytoskeleton in this system (3).…”

“…As shown in the cartoon in Fig. 6A, we speculate that the monomeric, motile, and lipid-binding conformation corresponds to a myosin-XXI fraction that has been localized at the base of the Leishmania flagellum (3,7). In contrast, the free, cytosolic dimeric fraction of myosin XXI might correspond to the detergent-labile component that has been localized within the flagellum where it could contribute to the structural organization of the actin network (3,7).…”

“…With lipid-binding sections along the converter, neck, and tail domain of the molecule, monomeric myosin XXI seems to be well suited to be targeted to lipid compartments with diverse lipid compositions. This might include the plasma membrane, but also organelles or vesicular cargo involved in intraflagellar transport, where myosin XXI might anchor these structures to and transport along the actin cytoskeleton (7). As shown in the cartoon in Fig.…”

“…Intriguingly, only myosin XXI was shown to be expressed in both the motile promastigote and the nonmotile amastigote stages of the parasite's life cycle (3). In the promastigote stage, this motor preferentially localized to the proximal part of the flagellum, although it was also found along the entire length of the flagellum and in other cell-body compartments (7). The myosin-XXI homozygous knockout is lethal.…”

“…The heterozygous cells were unable to form the paraflagellar rod, a structure of unknown function that runs along the length of the flagellum and contains a variety of proteins including actin and myosin XXI (8). It has also been reported that reduced expression levels cause the loss of endocytosis within the flagellar pocket and affect other intracellular trafficking processes (7). This makes myosin XXI an intriguing candidate to study modes of structural adaptation of a single myosin isoform for a variety of cellular acto-myosinbased motile functions.…”