title: Structural and functional differences of cytosolic 90-kDa heat-shock proteins (Hsp90s) in Arabidopsis thaliana.
abstract: The seven members of the 90-kDa heat shock protein (Hsp90) family encode highly conserved molecular chaperones essential for cell survival in Arabidopsis thaliana. Hsp90 are abundant proteins, localized in different compartments with AtHsp90.1-4 in the cytosol and AtHsp90.5-7 in different organelles. Among the AtHsp90, AtHsp90.1, is stress-inducible and shares comparatively low sequence identity with the constitutively expressed AtHsp90.2-4. Even though abundant information is available on mammalian cytosolic Hsp90 proteins, it is unknown whether cytosolic Hsp90 proteins display different structural and functional properties. We have now analyzed two A. thalianas cytosolic Hsp90s, AtHsp90.1 and AtHsp90.3, for functional divergence. AtHsp90.3 showed higher holdase chaperone activity than AtHsp90.1, although both AtHsp90s exhibited effective chaperone activity. Size-exclusion chromatography revealed different oligomeric states distinguishing the two Hsp90 proteins. While AtHsp90.1 exists in several oligomeric states, including monomers, dimers and higher oligomers, AtHsp90.3 exists predominantly in a high oligomeric state. High oligomeric state of AtHsp90.1 showed higher holdase chaperone activity than the respective monomer or dimer states. When high oligomeric forms of AtHsp90.1 and AtHsp90.3 are reduced by DTT, activity was reduced compared to that found in the native high oligomeric state. In addition, ATP-dependent foldase chaperone activity of AtHsp90.3 was higher with strong intrinsic ATPase activity than that of AtHsp90.1. As a conclusion, the two A. thaliana cytosolic Hsp90 proteins display different functional activities depending on structural differences, implying functional divergence although the proteins are localized to the same sub-cellular organelle.
authors.affiliation: Division of Applied Life Science (BK21 and WCU Program), Plant Molecular Biology and Biotechnology Research Center, Gyeongsang National University, Jinju 660-701, Republic of Korea.
authors.forename: Joon-Yung
authors.initials: JY
authors.lastname: Cha
authors.forename: Gyeongik
authors.initials: G
authors.lastname: Ahn
authors.forename: Joo Yeon
authors.initials: JY
authors.lastname: Kim
authors.forename: Sun Bin
authors.initials: SB
authors.lastname: Kang
authors.forename: Mi Ri
authors.initials: MR
authors.lastname: Kim
authors.forename: Mukhamad
authors.initials: M
authors.lastname: Su'udi
authors.forename: Woe-Yeon
authors.initials: WY
authors.lastname: Kim
authors.forename: Daeyoung
authors.initials: D
authors.lastname: Son
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D019281:Dimerization; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D018841:HSP90 Heat-Shock Proteins; D018832:Molecular Chaperones; D000255:Adenosine Triphosphate
keywords: Arabidopsis thaliana; Chaperone; Cytoplasm; G6PDH; HS; Heat shock protein 90; Hsps; MDH; Oligomerization; SEC; glucose-6-phosphate dehydrogenase; heat shock; heat shock proteins; malate dehydrogenase; size-exclusion chromatography