title: Plasmodium falciparum coronin organizes arrays of parallel actin filaments potentially guiding directional motility in invasive malaria parasites.
abstract: BACKGROUND
  Gliding motility in Plasmodium parasites, the aetiological agents of malaria disease, is mediated by an actomyosin motor anchored in the outer pellicle of the motile cell. Effective motility is dependent on a parasite myosin motor and turnover of dynamic parasite actin filaments. To date, however, the basis for directional motility is not known. Whilst myosin is very likely orientated as a result of its anchorage within the parasite, how actin filaments are orientated to facilitate directional force generation remains unexplained. In addition, recent evidence has questioned the linkage between actin filaments and secreted surface antigens leaving the way by which motor force is transmitted to the extracellular milieu unknown. Malaria parasites possess a markedly reduced repertoire of actin regulators, among which few are predicted to interact with filamentous (F)-actin directly. One of these, PF3D7_1251200, shows strong homology to the coronin family of actin-filament binding proteins, herein referred to as PfCoronin.
  
  
  METHODS
  Here the N terminal beta propeller domain of PfCoronin (PfCor-N) was expressed to assess its ability to bind and bundle pre-formed actin filaments by sedimentation assay, total internal reflection fluorescence (TIRF) microscopy and confocal imaging as well as to explore its ability to bind phospholipids. In parallel a tagged PfCoronin line in Plasmodium falciparum was generated to determine the cellular localization of the protein during asexual parasite development and blood-stage merozoite invasion.
  
  
  RESULTS
  A combination of biochemical approaches demonstrated that the N-terminal beta-propeller domain of PfCoronin is capable of binding F-actin and facilitating formation of parallel filament bundles. In parasites, PfCoronin is expressed late in the asexual lifecycle and localizes to the pellicle region of invasive merozoites before and during erythrocyte entry. PfCoronin also associates strongly with membranes within the cell, likely mediated by interactions with phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) at the plasma membrane.
  
  
  CONCLUSIONS
  These data suggest PfCoronin may fulfil a key role as the critical determinant of actin filament organization in the Plasmodium cell. This raises the possibility that macro-molecular organization of actin mediates directional motility in gliding parasites.
authors.affiliation: Infection and Immunity Division, Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, 3052, Australia. maya.olshina@gmail.com.|Department of Medical Biology, University of Melbourne, Parkville, VIC, 3052, Australia. maya.olshina@gmail.com.
authors.forename: Maya A
authors.initials: MA
authors.lastname: Olshina
authors.affiliation: Infection and Immunity Division, Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, 3052, Australia. fiona_angrisano@hotmail.com.|Department of Medical Biology, University of Melbourne, Parkville, VIC, 3052, Australia. fiona_angrisano@hotmail.com.
authors.forename: Fiona
authors.initials: F
authors.lastname: Angrisano
authors.affiliation: Infection and Immunity Division, Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, 3052, Australia. marapana@wehi.edu.au.|Department of Medical Biology, University of Melbourne, Parkville, VIC, 3052, Australia. marapana@wehi.edu.au.
authors.forename: Danushka S
authors.initials: DS
authors.lastname: Marapana
authors.affiliation: Infection and Immunity Division, Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, 3052, Australia. david_riglar@hms.harvard.edu.|Department of Medical Biology, University of Melbourne, Parkville, VIC, 3052, Australia. david_riglar@hms.harvard.edu.|Department of Systems Biology, Harvard Medical School, 200 Longwood Ave WAB 536, Boston, MA, 02115, USA. david_riglar@hms.harvard.edu.
authors.forename: David T
authors.initials: DT
authors.lastname: Riglar
authors.affiliation: Department of Infectious Diseases, University of Heidelberg Medical School, Heidelberg, Germany. kartikbane@gmail.com.
authors.forename: Kartik
authors.initials: K
authors.lastname: Bane
authors.affiliation: Infection and Immunity Division, Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, 3052, Australia. wwong@wehi.edu.au.|Department of Medical Biology, University of Melbourne, Parkville, VIC, 3052, Australia. wwong@wehi.edu.au.
authors.forename: Wilson
authors.initials: W
authors.lastname: Wong
authors.affiliation: Ludwig Institute for Cancer Research, Melbourne Tumour Biology Branch, Royal Melbourne Hospital, Parkville, VIC, 3052, Australia. bruno.catimel@ludwig.edu.au.|Systems Biology and Personalised Medicine Division, Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, 3052, Australia. bruno.catimel@ludwig.edu.au.
authors.forename: Bruno
authors.initials: B
authors.lastname: Catimel
authors.affiliation: School of Chemistry, Bio21 Institute, University of Melbourne, Parkville, VIC, 3010, Australia. mengxiny@gmail.com.
authors.forename: Meng-Xin
authors.initials: MX
authors.lastname: Yin
authors.affiliation: School of Chemistry, Bio21 Institute, University of Melbourne, Parkville, VIC, 3010, Australia. aholmes@unimelb.edu.au.
authors.forename: Andrew B
authors.initials: AB
authors.lastname: Holmes
authors.affiliation: Department of Infectious Diseases, University of Heidelberg Medical School, Heidelberg, Germany. fratsch@gmail.com.
authors.forename: Friedrich
authors.initials: F
authors.lastname: Frischknecht
authors.affiliation: Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, USA. drkovar@uchicago.edu.|Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, USA. drkovar@uchicago.edu.
authors.forename: David R
authors.initials: DR
authors.lastname: Kovar
authors.affiliation: Infection and Immunity Division, Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, 3052, Australia. jake.baum@imperial.ac.uk.|Department of Medical Biology, University of Melbourne, Parkville, VIC, 3052, Australia. jake.baum@imperial.ac.uk.|Department of Life Sciences, Imperial College London, Sir Alexander Fleming Building, Level 6, South Kensington, London, SW72AZ, UK. jake.baum@imperial.ac.uk.
authors.forename: Jake
authors.initials: J
authors.lastname: Baum
mesh_terms: D008841:Actin Cytoskeleton / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D004912:Erythrocytes / Q000469:parasitology; D006801:Humans; D016778:Malaria, Falciparum / Q000469:parasitology; D008840:Microfilament Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D010963:Plasmodium falciparum / Q000737:chemistry* / Q000378:metabolism / Q000472:pathogenicity / Q000502:physiology*; D015800:Protozoan Proteins / Q000737:chemistry* / Q000378:metabolism; D011817:Rabbits
chemical_list: D008840:Microfilament Proteins; D015800:Protozoan Proteins; C072061:coronin proteins