PMID:23397569

Citation	Lee, JY, Song, SM, Moon, EK, Lee, YR, Jha, BK, Danne, DB, Cha, HJ, Yu, HS, Kong, HH, Chung, DI and Hong, Y (2013) Cysteine Protease Inhibitor (AcStefin) Is Required for Complete Cyst Formation of Acanthamoeba. Eukaryotic Cell 12:567-74
Abstract	The encystation of Acanthamoeba 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 Acanthamoeba from intracellular damage. However, mechanisms underlying the control of protease activity during encystation have not been established in Acanthamoeba. In the present study, we identified and characterized Acanthamoeba 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 Acanthamoeba.
Links	PubMed Online version:10.1128/EC.00308-12
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
ACACA:G8IIS4		GO:0030414: peptidase inhibitor activity	ECO:0000314:		F		Figure 1B and 1C show that the cysteine protease inhibitor inhibited human cathepsin L, human cathepsin B, and papain enzymes. All of these enzymes are part of the C1 family of cysteine proteinases, therefore showing that the cysteine protease inhibitor inhibits protease, or peptidase, activity.	complete CACAO 7629
ACACA:G8IIS4		GO:0005764: lysosome	ECO:0000314:		C		Figure two shows that the cysteine protease inhibitor, originally located in the cytoplasm, localizes to the lysosome during cyst formation.	complete CACAO 7632
ACACA:G8IIS4	enables	GO:0030414: peptidase inhibitor activity	ECO:0000314: direct assay evidence used in manual assertion		F		Seeded From UniProt	complete
ACACA:G8IIS4	part_of	GO:0005764: lysosome	ECO:0000314: direct assay evidence used in manual assertion		C		Seeded From UniProt	complete

References

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