{"doi":"10.1016/j.jbc.2024.108101","title":"Bending stiffness of Toxoplasma gondii actin filaments","abstract":"Actin is essential for the survival and pathogenicity of the Apicomplexan parasite Toxoplasma gondii , where it plays essential functions in cargo transport, invasion, egress, and organelle inheritance. Recent work has shown that, unlike vertebrate skeletal muscle actin, purified T . gondii actin filaments (TgAct1) can undergo rapid treadmilling, due to large differences in the barbed- and pointed-end critical concentrations, rapid subunit dissociation from filament ends, and a rapid nucleotide exchange rate constant from free monomers. Previous structural analysis suggested that the unique assembly properties of TgAct1 filaments may be a functional consequence of reduced contacts between the DNAse-1–binding loop (D-loop) of a filament subunit and its adjacent, long-axis subunit neighbor. Because the D-loop makes stabilizing interactions between neighboring subunits, it has been implicated in regulating the mechanical properties of actin filaments. In this study, we measured the bending persistence length ( L B ) of TgAct1 filaments and the filament length distribution. We found that despite compromised intersubunit D-loop contacts, TgAct1 filaments have similar bending stiffness and thermodynamic stability as vertebrate actin filaments. Analysis of published cryo-EM image density maps indicates that TgAct1 filaments retain a stabilizing intersubunit salt bridge between E168 and K62 and reveals visible density between Y167 and S61 of adjacent filament subunits, consistent with a conserved cation binding site proximal to the D-loop, as initially identified in vertebrate skeletal muscle actin filaments. These results favor a mechanism in which weak D-loop interactions compromise TgAct1 subunit incorporation at filament ends, while minimally affecting overall subunit interactions within filaments.","journal":"Journal of Biological Chemistry","year":2024,"id":482692,"datarank":0.0,"base_score":0.0,"endowment":0.0,"self_citation_contribution":0.0,"citation_network_contribution":0.0,"self_endowment_contribution":0.0,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":1,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.9527,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2024-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":585762,"name":"Thomas E. Sladewski","orcid":"0000-0002-8584-5007","position":1,"is_corresponding":false},{"id":1177062,"name":"Aoife T. Heaslip","orcid":"0000-0002-7838-3617","position":2,"is_corresponding":false},{"id":308722,"name":"Enrique M. De La Cruz","orcid":"0000-0003-4798-2892","position":3,"is_corresponding":false},{"id":308718,"name":"Wenxiang Cao","orcid":"0009-0001-3638-9586","position":0,"is_corresponding":true}],"reference_count":54,"raw_metadata":null,"created_at":"2026-07-19T02:07:18.280369Z","pmid":"39706262","pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}