The Lasso Segment Is Required for Functional Dimerization of the Plasmodium Formin 1 FH2 Domain

Abstract

Apicomplexan parasites, such as the malaria-causing Plasmodium species, utilize a unique way of locomotion and host cell invasion. This substrate-dependent gliding motility requires rapid cycling of actin between the monomeric state and very short, unbranched filaments. Despite the crucial role of actin polymerization for the survival of the malaria parasite, the majority of Plasmodium cellular actin is present in the monomeric form. Plasmodium lacks most of the canonical actin nucleators, and formins are essentially the only candidates for this function in all Apicomplexa. The malaria parasite has two formins, containing conserved formin homology (FH) 2 and rudimentary FH1 domains. Here, we show that Plasmodium falciparum formin 1 associates with and nucleates both mammalian and Plasmodium actin filaments. Although Plasmodium profilin alone sequesters actin monomers, thus inhibiting polymerization, its monomer-sequestering activity does not compete with the nucleating activity of formin 1 at an equimolar profilin-actin ratio. We have determined solution structures of P. falciparum formin 1 FH2 domain both in the presence and absence of the lasso segment and the FH1 domain, and show that the lasso is required for the assembly of functional dimers.

Juxtanodin is an intrinsically disordered F-actin-binding protein

“…Skeletal muscle actin was prepared from the loin of pig and further purified as described previously5657. The pig loins were gifts from the University of Oulu Laboratory Animal Centre and were from animals used in other animal experiments with separate licenses from the Finnish National Animal Experiment Board.…”

Structure of Toxoplasma gondii coronin, an actin‐binding protein that relocalizes to the posterior pole of invasive parasites and contributes to invasion and egress

“…Pig skeletal muscle ␣-actin was purified as described previously (13,53). Purified actin was stored up to 1 wk in dialysis against depolymerizing buffer (G buffer), containing 5 mM Tris-HCl (pH 8), 0.2 mM CaCl 2 , 0.2 mM ATP, and 0.5 mM DTT, and the buffer was changed daily, to replenish the ATP and DTT.…”

Organization and function of an actin cytoskeleton inPlasmodium falciparumgametocytes

“…The only candidates for actin‐bundling proteins are the WD40 repeat containing protein, coronin (Clemen et al ., ), which has been found in association with F‐actin in P. falciparum schizonts (Tardieux et al ., ), and the α and β subunits of the capping protein, which stabilizes actin filaments by barbed‐end capping (Kim et al ., ; Cooper and Sept, ; Ganter et al ., ). Formin‐1 is of particular interest; it displays barbed‐end nucleator activity in vitro and is apically located in merozoites, consistent with a role in promoting actin polymerization at this site (Baum et al ., ; Ignatev et al ., ).…”

“…Apicomplexan genomes encode a strikingly small repertoire of polymerization-promoting proteins compared with other eukaryotes (Baum et al, 2006;Schuler and Matuschewski, 2006). They lack classical regulators such as the Arp2/3 complex, but encode two formin homology proteins (formin-1 and formin-2) (Baum et al, 2008;Ignatev et al, 2012). The only candidates for actinbundling proteins are the WD40 repeat containing protein, coronin (Clemen et al, 2008), which has been found in association with F-actin in P. falciparum schizonts (Tardieux et al, 1998), and the α and β subunits of the capping protein, which stabilizes actin filaments by barbed-end capping (Kim et al, 2007;Cooper and Sept, 2008;Ganter et al, 2009).…”