Identification of Actin Filament-Associated Proteins in Giardia lamblia. 2021

Melissa C Steele-Ogus, and Richard S Johnson, and Michael J MacCoss, and Alexander R Paredez
Department of Biology, University of Washingtongrid.34477.33, Seattle, Washington, USA.

The deep-branching protozoan parasite Giardia lamblia is the causative agent of the intestinal disease giardiasis. Consistent with its proposed evolutionary position, many pathways are minimalistic or divergent, including its actin cytoskeleton. Giardia is the only eukaryote known to lack all canonical actin-binding proteins. Previously, our lab identified a number of noncanonical Giardia lamblia actin (GlActin) interactors; however, these proteins appeared to interact only with monomeric or globular actin (G-actin) rather than with filamentous actin (F-actin). To identify F-actin interactors, we used a chemical cross-linker to preserve native interactions followed by an anti-GlActin antibody, protein A affinity chromatography, and liquid chromatography coupled to mass spectrometry. We found 46 putative actin interactors enriched under the conditions favoring F-actin. Data are available via ProteomeXchange with identifier PXD026067. None of the proteins identified contain known actin-interacting motifs, and many lacked conserved domains. Each potential interactor was then tagged with the fluorescent protein mNeonGreen and visualized in live cells. We categorized the proteins based on their primary localization; localizations included ventral disc, marginal plate, nuclei, flagella, plasma membrane, and internal membranes. One protein from each of the six categories was colocalized with GlActin using immunofluorescence microscopy. We also co-immunoprecipitated one protein from each category and confirmed three of the six potential interactions. Most of the localization patterns are consistent with previously demonstrated GlActin functions, but the ventral disc represents a new category of actin interactor localization. These results suggest a role for GlActin in ventral disc function, which has previously been controversial. IMPORTANCE Giardia lamblia is an intestinal parasite that colonizes the small intestine and causes diarrhea, which can lead to dehydration and malnutrition. Giardia actin (GlActin) has a conserved role in Giardia cells, despite being a highly divergent protein with none of the conserved regulators found in model organisms. Here, we identify and localize 46 interactors of polymerized actin. These putative interactors localize to a number of places in the cell, underlining GlActin's importance in multiple cellular processes. Surprisingly, eight of these proteins localize to the ventral disc, Giardia's host attachment organelle. Since host attachment is required for infection, proteins involved in this process are an appealing target for new drugs. While treatments for Giardia exist, drug resistance is becoming more common, resulting in a need for new treatments. Giardia and human systems are highly dissimilar, thus drugs specifically tailored to Giardia proteins would be less likely to have side effects.

UI MeSH Term Description Entries
D008840 Microfilament Proteins Monomeric subunits of primarily globular ACTIN and found in the cytoplasmic matrix of almost all cells. They are often associated with microtubules and may play a role in cytoskeletal function and/or mediate movement of the cell or the organelles within the cell. Actin Binding Protein,Actin-Binding Protein,Actin-Binding Proteins,Microfilament Protein,Actin Binding Proteins,Binding Protein, Actin,Protein, Actin Binding,Protein, Actin-Binding,Protein, Microfilament,Proteins, Actin-Binding,Proteins, Microfilament
D011485 Protein Binding The process in which substances, either endogenous or exogenous, bind to proteins, peptides, enzymes, protein precursors, or allied compounds. Specific protein-binding measures are often used as assays in diagnostic assessments. Plasma Protein Binding Capacity,Binding, Protein
D005873 Giardiasis An infection of the SMALL INTESTINE caused by the flagellated protozoan GIARDIA. It is spread via contaminated food and water and by direct person-to-person contact. Lambliasis,Giardia Infection,Giardia duodenalis Infection,Giardia intestinalis Infection,Giardia lamblia Infection,Giardia Infections,Giardia duodenalis Infections,Giardia intestinalis Infections,Giardia lamblia Infections,Giardiases,Infection, Giardia,Infection, Giardia duodenalis,Infection, Giardia intestinalis,Infection, Giardia lamblia,Infections, Giardia,Infections, Giardia duodenalis,Infections, Giardia intestinalis,Infections, Giardia lamblia,Lambliases
D006790 Host-Parasite Interactions The relationship between an invertebrate and another organism (the host), one of which lives at the expense of the other. Traditionally excluded from definition of parasites are pathogenic BACTERIA; FUNGI; VIRUSES; and PLANTS; though they may live parasitically. Host-Parasite Relations,Parasite-Host Relations,Host-Parasite Relationship,Parasite-Host Interactions,Host Parasite Interactions,Host Parasite Relations,Host Parasite Relationship,Host-Parasite Interaction,Host-Parasite Relation,Host-Parasite Relationships,Interaction, Host-Parasite,Interaction, Parasite-Host,Interactions, Host-Parasite,Interactions, Parasite-Host,Parasite Host Interactions,Parasite Host Relations,Parasite-Host Interaction,Parasite-Host Relation,Relation, Host-Parasite,Relation, Parasite-Host,Relations, Host-Parasite,Relations, Parasite-Host,Relationship, Host-Parasite,Relationships, Host-Parasite
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000199 Actins Filamentous proteins that are the main constituent of the thin filaments of muscle fibers. The filaments (known also as filamentous or F-actin) can be dissociated into their globular subunits; each subunit is composed of a single polypeptide 375 amino acids long. This is known as globular or G-actin. In conjunction with MYOSINS, actin is responsible for the contraction and relaxation of muscle. F-Actin,G-Actin,Actin,Isoactin,N-Actin,alpha-Actin,alpha-Isoactin,beta-Actin,gamma-Actin,F Actin,G Actin,N Actin,alpha Actin,alpha Isoactin,beta Actin,gamma Actin
D015800 Protozoan Proteins Proteins found in any species of protozoan. Proteins, Protozoan
D016829 Giardia lamblia A species of parasitic EUKARYOTES that attaches itself to the intestinal mucosa and feeds on mucous secretions. The organism is roughly pear-shaped and motility is somewhat erratic, with a slow oscillation about the long axis. Giardia duodenalis,Giardia intestinalis,Lamblia intestinalis,Giardia lamblias

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