{"doi":"10.1128/ec.00308-12","title":"Cysteine Protease Inhibitor (AcStefin) Is Required for Complete Cyst Formation of Acanthamoeba","abstract":"<jats:title>ABSTRACT</jats:title>\n          <jats:p>\n            The encystation of\n            <jats:named-content content-type=\"genus-species\">Acanthamoeba</jats:named-content>\n            leads to the formation of resilient cysts from vegetative trophozoites. This process is essential for parasite survival under unfavorable conditions, such as those associated with starvation, low temperatures, and biocides. Furthermore, cysteine proteases have been implicated in the massive turnover of intracellular components required for encystation. Thus, strict modulation of the activities of cysteine proteases is required to protect\n            <jats:named-content content-type=\"genus-species\">Acanthamoeba</jats:named-content>\n            from intracellular damage. However, mechanisms underlying the control of protease activity during encystation have not been established in\n            <jats:named-content content-type=\"genus-species\">Acanthamoeba</jats:named-content>\n            . In the present study, we identified and characterized\n            <jats:named-content content-type=\"genus-species\">Acanthamoeba</jats:named-content>\n            cysteine protease inhibitor (AcStefin), which was found to be highly expressed during encystation and to be associated with lysosomes by fluorescence microscopy. Recombinant AcStefin inhibited various cysteine proteases, including human cathepsin B, human cathepsin L, and papain. Transfection with small interfering RNA against AcStefin increased cysteine protease activity during encystation and resulted in incomplete cyst formation, reduced excystation efficiency, and a significant reduction in cytoplasmic area. Taken together, these results indicate that AcStefin is involved in the modulation of cysteine proteases and that it plays an essential role during the encystation of\n            <jats:named-content content-type=\"genus-species\">Acanthamoeba</jats:named-content>\n            .\n          </jats:p>","journal":"Eukaryotic 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and Acanthamoeba research","Heme Oxygenase-1 and Carbon Monoxide","Neutrophil, Myeloperoxidase and Oxidative Mechanisms","Biology","Medicine","Acanthamoeba castellanii","Amino Acid Sequence","Animals","Cathepsins","Cystatins","Cysteine Proteases","Cysteine Proteinase Inhibitors","Gene Expression Regulation","Gene Silencing","Humans","Life Cycle Stages","Lysosomes","Molecular Sequence Data","Protozoan Proteins","RNA, Small Interfering","Recombinant Proteins","Sequence Alignment"],"mesh_terms":["Amino Acid Sequence","Animals","Cathepsins","Gene Expression Regulation","Humans","Life Cycle Stages","Lysosomes","Molecular Sequence Data","Recombinant Proteins","Protozoan Proteins","Cysteine Proteinase Inhibitors","Cystatins","Sequence Alignment","Gene Silencing","RNA, Small Interfering","Acanthamoeba castellanii","Cysteine Proteases"],"keywords":["Biology","Cysteine protease","Acanthamoeba","Cysteine","Protease inhibitor (pharmacology)","Protease","Biochemistry","Cysteine Proteinase Inhibitors","Protozoa","Microbiology","Enzyme","Genetics","Caspase","Virus"],"sdg_mappings":[],"linked_datasets":[],"clinical_trials":[],"software_tools":[],"database_accessions":[{"name":"gen"}],"source":"live","citation_network_status":"fetched"},"created_at":"2026-06-09T17:30:02.382255Z","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":[]}