{"doi":"10.1101/2025.05.15.654217","title":"Interplay between SpaO variants shapes the architecture of the <i>Salmonella</i> type III secretion sorting platform","abstract":"Abstract Salmonella enterica utilizes a virulence-associated type III secretion system (T3SS) to inject bacterial effectors directly into host cells. Central to this machinery is the sorting platform (SP), a cytosolic assembly whose core scaffolding protein, SpaO, is produced in two isoforms: a full-length (SpaO L ) and a shorter variant (SpaO short ) comprising the C-terminal 101 residues of SpaO L . Although SpaO short is evolutionarily conserved across type III secretion systems, its precise function has remained elusive. Here, we combined a sensitive, real-time translocation assay with site-directed photo-crosslinking to elucidate the role of SpaO short in Salmonella SPI-1 T3SS. We found that while SpaO short is not absolutely required for effector secretion, its absence significantly dampens T3SS-mediated protein delivery. Further biochemical and structural probing revealed that SpaO short is a structural component of the sorting platform, arranged as a homodimer associated to SpaO L via an N-terminal “docking motif.” This interaction occurs while SpaO L is associated with other SP components, supporting a model in which SpaO short is integrated into the SP pods alongside SpaO L , OrgA, and OrgB. Collectively, these findings show that SpaO short , while not strictly essential, functions as a critical structural component of the sorting platform, providing new insights into how Salmonella and related bacteria assemble and maintain these specialized protein-injection systems.","journal":"bioRxiv (Cold Spring Harbor Laboratory)","year":2025,"id":556314,"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":2,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.955,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2025-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":1455591,"name":"Tingting Wang","orcid":"0000-0001-8051-405X","position":1,"is_corresponding":false},{"id":1036988,"name":"Jorge E. Galán","orcid":"0000-0002-6531-0355","position":2,"is_corresponding":false},{"id":1036987,"name":"Marı́a Lara-Tejero","orcid":"0000-0002-1339-0859","position":3,"is_corresponding":false},{"id":1455590,"name":"Eduardo Soto","orcid":"0000-0002-6954-479X","position":0,"is_corresponding":true}],"reference_count":44,"raw_metadata":null,"created_at":"2026-07-19T02:55:08.896385Z","pmid":"40463283","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":[]}