{"doi":"10.1101/2022.06.02.493408","title":"Osmotic stress response in BetP: How lipids and K <sup>+</sup> team up to overcome downregulation","abstract":"Abstract The trimeric betaine symporter BetP senses an osmotic upshift via its osmosensory C-terminal domain and responds rapidly with a steep increase in transport rate. Full activation requires both an elevated internal K + concentration and a yet unknown membrane stimulus. Moreover, the molecular mechanisms of stress sensing and upregulation remain unclear. Here, we show that K + binding to BetP in vivo is highly cooperative. Using X-ray crystallography, we identify four putative K + interaction sites at the C-terminal domains of BetP. Single particle CryoEM on BetP reconstituted in amphipols (AMP-BetP), in the absence of K + , revealed that the three C-terminal domains are oriented symmetrically near the membrane surface, representing a new downregulated state. The presence of K + resulted in asymmetric partial unfolding of the C-terminal domains, which was assigned as an intermediate between the downregulated state and the conformation observed in crystal structures. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy in 2D crystals of BetP reveal glutamate/aspartate and tyrosine responses to K + , in agreement with the identified K + interaction sites, as well as specific unfolding events in the C-terminal domain upon activation. A rearrangement of the relative protomer orientations confers upregulation through key structural elements involved in the alternating access of BetP affecting sodium and betaine binding affinities. Although K + -specific regulation is unique to BetP we discuss unfolding/refolding of sensory domains as a unifying element in hyperosmotic stress response of osmoregulated transporters.","journal":"bioRxiv (Cold Spring Harbor Laboratory)","year":2022,"id":301394,"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":0.9568,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2022-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":992530,"name":"Günnur Güler","orcid":"0000-0002-8485-7372","position":1,"is_corresponding":false},{"id":563133,"name":"Vanessa Leone","orcid":"0000-0001-7017-4020","position":2,"is_corresponding":false},{"id":298025,"name":"Mariusz Madej","orcid":"0000-0002-9935-3871","position":3,"is_corresponding":false},{"id":992919,"name":"Stanislav Maksimov","orcid":null,"position":4,"is_corresponding":false},{"id":992920,"name":"Rebecca M. Gärtner","orcid":null,"position":5,"is_corresponding":false},{"id":992921,"name":"Olga Rudi","orcid":null,"position":6,"is_corresponding":false},{"id":655108,"name":"Farzad Hamdi","orcid":"0000-0002-2155-5000","position":7,"is_corresponding":false},{"id":314549,"name":"Panagiotis L. Kastritis","orcid":"0000-0002-1463-8422","position":8,"is_corresponding":false},{"id":992531,"name":"Werner Mäntele","orcid":"0000-0003-4136-7151","position":9,"is_corresponding":false},{"id":992922,"name":"Reinhard Krämer","orcid":null,"position":10,"is_corresponding":false},{"id":307888,"name":"Lucy R. Forrest","orcid":"0000-0003-1855-7985","position":11,"is_corresponding":false},{"id":992532,"name":"Camilo Pérez","orcid":"0000-0002-5800-0084","position":12,"is_corresponding":false},{"id":982399,"name":"Christine Ziegler","orcid":"0000-0003-3439-7213","position":13,"is_corresponding":false},{"id":982398,"name":"Veronika Heinz","orcid":"0000-0003-4084-7460","position":0,"is_corresponding":true}],"reference_count":46,"raw_metadata":null,"created_at":"2026-07-19T00:32:02.193874Z","pmid":null,"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":[]}