Identification of Actin Filament-Associated Proteins in Giardia lamblia.

{"sci_version": "1.2", "schema": "https://corpus.bntrg.co.uk/sci/1.0/sci.schema.json", "id": "pmid:34287056", "kind": "science-record", "revision": 6, "content_hash": "sha256:218dcc147b876d278115ca1d5e7699023234de9fc6f922a8faba92eb17033dbf", "created_at": "2026-11-01T15:41:44Z", "updated_at": "2026-11-01T21:25:49Z", "generator": {"name": "corpus-assay-engine", "run_id": "reading-sci-2026-11-01"}, "paper": {"state": "complete", "title": "Identification of Actin Filament-Associated Proteins in Giardia lamblia.", "doi": "10.1128/Spectrum.00558-21", "pmid": "34287056", "authors": ["Melissa C Steele-Ogus", "Richard S Johnson", "Michael J MacCoss", "Alexander R Paredez"], "journal": "Microbiology spectrum", "year": 2021, "abstract": "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. 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plasma membrane"], ["GL50803_17255", "Hypothetical", "Plasma membrane, flange, basal bodies"], ["GL50803_5810", "Hypothetical", "Plasma membrane"], ["GL50803_11684", "Leucine-rich repeat protein", "Plasma membrane"], ["Internal membrane localization", "", ""], ["GL50803_9861", "Hypothetical", "Diffuse internal membrane"], ["GL50803_13930", "Arf3", "Puncta"], ["GL50803_22855", "Hypothetical", "Vesicles"], ["GL50803_12999", "Hypothetical", "Puncta and unidentified compartment"], ["Marginal plate localization", "", ""], ["GL50803_17153", "Alpha-11 giardin", "Marginal plate and axonemal-associated structures"], ["GL50803_115478", "Ankyrin repeat, takusan, SMC", "Marginal plate and flagellar exit sites"], ["GL50803_8854", "Hypothetical", "Marginal plate and flagellar exit sites"], ["GL50803_4383", "Ankyrin repeat", "Marginal plate and axonemal-associated structures"], ["GL50803_5800", "Hypothetical", "Marginal plate and puncta"], ["GL50803_9030", "Ankyrin repeat", "Marginal plate and cytoplasmic puncta"], ["GL50803_16522", "Hypothetical", "Cytoplasmic, marginal disc, nuclei"], ["Nuclear localization", "", ""], ["GL50803_101212", "Hypothetical", "Perinuclear region"], ["GL50803_33989", "Hypothetical", "Puncta and filaments within nucleus"], ["GL50903_14299", "Hypothetical", "Diffuse nuclear localization with puncta"], ["GL50803_5328", "Sigma adaptin (AP-2 complex)", "Diffuse nuclear localization and plasma membrane"], ["GL50803_102813", "Ankyrin repeat", "Nuclear, marginal plate, cytoplasmic"], ["GL50803_14213", "Hypothetical", "Diffuse nuclear localization with puncta"], ["Flagellar localization", "", ""], ["GL50803_9848", "Dynein light chain", "Internal portions of flagella, basal bodies"], ["GL50803_33685", "Armadillo repeat", "Flagella"], ["GL50803_15097", "Alpha-14 giardin", "Flagella"], ["GL50803_13774", "Hypothetical", "Flagellar exit sites"], ["GL50803_4463", "Dynein light chain", "Flagella"], ["GL50803_15124", "Dynein light chain", "Flagella"], ["Disc 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We found 46 putative actin interactors enri", "HODS Purification and sample preparation for mass spectrometry. Lysates were incubated overnight with an an", "digestion. Supernatant was then removed for LC-MS/MS analysis. Protein was further extracted from", "esuspended in solvent A and then analyzed by LC-MS/MS as described below. Supplementary Materials"], "order_basis": "paper_text_order:803", "id": "assay:1"}, {"role": "data_generation", "definition_id": "ihc", "definition_version": "99e1195c7d6f", "definition_digest": null, "required_operations": [], "support_state": "partial", "source_hashes": {"assay_lexicon": "99e1195c7d6f"}, "confidence": 0.93, "evidence": ["ategories was colocalized with GlActin using immunofluorescence microscopy. We also co-immunoprecipitated on"], "order_basis": "paper_text_order:1450", "id": "assay:2"}]}