A unique profilin-actin interface is important for malaria parasite motility

Abstract

<div lang="en" class="abs"><p class="abs_header">Abstract</p><p>Profilin is an actin monomer binding protein that provides ATP-actin for incorporation into actin filaments. In contrast to higher eukaryotic cells with their large filamentous actin structures, apicomplexan parasites typically contain only short and highly dynamic microfilaments. In apicomplexans, profilin appears to be the main monomer-sequestering protein. Compared to classical profilins, apicomplexan profilins contain an additional arm-like β-hairpin motif, which we show here to be critically involved in actin binding. Through comparative analysis using two profilin mutants, we reveal this motif to be implicated in gliding motility of Plasmodium berghei sporozoites, the rapidly migrating forms of a rodent malaria parasite transmitted by mosquitoes. Force measurements on migrating sporozoites and molecular dynamics simulations indicate that the interaction between actin and profilin fine-tunes gliding motility. Our data suggest that evolutionary pressure to achieve efficient high-speed gliding has resulted in a unique profilin-actin interface in these parasites.</p></div>

<div lang="en" class="abs"><p class="abs_header">Author summary</p><p>The malaria parasite <em>Plasmodium</em> has two invasive forms that migrate across different tissue barriers, the ookinete and the very rapidly migrating sporozoite. Previous work has shown that the motility of these and related parasites (e.g. <em>Toxoplasma gondii</em>) depends on a highly dynamic actin cytoskeleton and retrograde flow of surface adhesins. These unusual actin dynamics are due to the divergent structure of protozoan actins and the actions of actin-binding proteins, which can have non-canonical functions in these parasites. Profilin is one of the most important and most investigated actin-binding proteins, which binds ADP-actin and catalyzes ADP-ATP exchange to then promote actin polymerization. Parasite profilins bind monomeric actin and contain an additional domain compared to canonical profilins. Here we show that this additional domain of profilin is critical for actin binding and rapid sporozoite motility but has little impact on the slower ookinete. Sporozoites of a parasite line carrying mutations in this domain cannot translate force production and retrograde flow into optimal parasite motility. Using molecular dynamics simulations, we find that differences between mutant parasites in their capacity to migrate can be traced back to a single hydrogen bond at the actin-profilin interface.</p></div>