title: Minimal requirements for actin filament disassembly revealed by structural analysis of malaria parasite actin-depolymerizing factor 1.
abstract: Malaria parasite cell motility is a process that is dependent on the dynamic turnover of parasite-derived actin filaments. Despite its central role, actin's polymerization state is controlled by a set of identifiable regulators that is markedly reduced compared with those of other eukaryotic cells. In Plasmodium falciparum, the most virulent species that affects humans, this minimal repertoire includes two members of the actin-depolymerizing factor/cofilin (AC) family of proteins, P. falciparum actin-depolymerizing factor 1 (PfADF1) and P. falciparum actin-depolymerizing factor 2. This essential class of actin regulator is involved in the control of filament dynamics at multiple levels, from monomer binding through to filament depolymerization and severing. Previous biochemical analyses have suggested that PfADF1 sequesters monomeric actin but, unlike most eukaryotic counterparts, has limited potential to bind or depolymerize filaments. The molecular basis for these unusual properties and implications for parasite cell motility have not been established. Here we present the crystal structure of an apicomplexan AC protein, PfADF1. We show that PfADF1 lacks critical residues previously implicated as essential for AC-mediated actin filament binding and disassembly, having a substantially reduced filament-binding loop and C-terminal α4 helix. Despite this divergence in structure, we demonstrate that PfADF1 is capable of efficient actin filament severing. Furthermore, this severing occurs despite PfADF1's low binding affinity for filaments. Comparative structural analysis along with biochemical and microscopy evidence establishes that severing is reliant on the availability of an exposed basic residue in the filament-binding loop, a conserved minimal requirement that defines AC-mediated filament disassembly across eukaryotic cells.
authors.affiliation: Infection and Immunity Division, The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia.
authors.forename: Wilson
authors.initials: W
authors.lastname: Wong
authors.forename: Colleen T
authors.initials: CT
authors.lastname: Skau
authors.forename: Danushka S
authors.initials: DS
authors.lastname: Marapana
authors.forename: Eric
authors.initials: E
authors.lastname: Hanssen
authors.forename: Nicole L
authors.initials: NL
authors.lastname: Taylor
authors.forename: David T
authors.initials: DT
authors.lastname: Riglar
authors.forename: Elizabeth S
authors.initials: ES
authors.lastname: Zuccala
authors.forename: Fiona
authors.initials: F
authors.lastname: Angrisano
authors.forename: Heather
authors.initials: H
authors.lastname: Lewis
authors.forename: Bruno
authors.initials: B
authors.lastname: Catimel
authors.forename: Oliver B
authors.initials: OB
authors.lastname: Clarke
authors.forename: Nadia J
authors.initials: NJ
authors.lastname: Kershaw
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Perugini
authors.forename: David R
authors.initials: DR
authors.lastname: Kovar
authors.forename: Jacqueline M
authors.initials: JM
authors.lastname: Gulbis
authors.forename: Jake
authors.initials: J
authors.lastname: Baum
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D051339:Actin Depolymerizing Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000199:Actins / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D018360:Crystallography, X-Ray; D006801:Humans; D015151:Immunoblotting; D008288:Malaria / Q000469:parasitology; D008856:Microscopy, Fluorescence / Q000379:methods; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D010963:Plasmodium falciparum / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
chemical_list: D051339:Actin Depolymerizing Factors; D000199:Actins; D015800:Protozoan Proteins