Alpha-crystallin and ATP facilitate the in vitro renaturation of xylanase: enhancement of refolding by metal ions.
Alpha-crystallin is a multimeric protein that functions as a molecular chaperone and shares extensive structural homology to small heat shock proteins. For the functional in vitro analysis of alpha-crystallin, the xylanase Xyl II from alkalophilic thermophilic Bacillus was used as a model system. The mechanism of chaperone action of alpha-crystallin is less investigated. Here we studied the refolding of Gdn HCl-denatured Xyl II in the presence and absence of alpha-crystallin to elucidate the molecular mechanism of chaperone-mediated in vitro folding. Our results, based on intrinsic tryptophan fluorescence and hydrophobic fluorophore 8-anilino-1-naphthalene sulfonate binding studies, suggest that alpha-crystallin formed a complex with a putative molten globule-like intermediate in the refolding pathway of Xyl II. The alpha-crystallin.Xyl II complex exhibited no functional activity. Addition of ATP to the complex initiated the renaturation of Xyl II with 30%-35% recovery of activity. The nonhydrolyzable analog 5'-adenylyl imidodiphosphate (AMP-PNP) was capable of reconstitution of active Xyl II to a lesser extent than ATP. Although the presence of Ca(2+) was not required for the in vitro refolding of Xyl II, the renaturation yield was enhanced in its presence. Experimental evidence indicated that the binding of ATP to the alpha-crystallin.Xyl II complex brought about conformational changes in alpha-crystallin facilitating the dissociation of xylanase molecules. This is the first report of the enhancement of alpha-crystallin chaperone functions by metal ions.
Nath
Devyani
D
Biochemical Sciences Division, National Chemical Laboratory, Pashan Pune-411 008, India.
Rawat
Urmila
U
Anish
Ramakrishnan
R
Rao
Mala
M
D000255:Adenosine Triphosphate / Q000378:metabolism*; D001407:Bacillus / Q000201:enzymology; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D004789:Enzyme Activation; D007477:Ions / Q000737:chemistry / Q000378:metabolism; D008670:Metals / Q000737:chemistry / Q000378:metabolism*; D018832:Molecular Chaperones / Q000737:chemistry / Q000378:metabolism; D011489:Protein Denaturation; D017510:Protein Folding; D020673:Protein Renaturation; D013050:Spectrometry, Fluorescence; D013696:Temperature; D043325:Xylan Endo-1,3-beta-Xylosidase; D014995:Xylosidases / Q000737:chemistry* / Q000378:metabolism; D038201:alpha-Crystallins / Q000378:metabolism*
D001426:Bacterial Proteins; D007477:Ions; D008670:Metals; D018832:Molecular Chaperones; D038201:alpha-Crystallins; D000255:Adenosine Triphosphate; D014995:Xylosidases; D043325:Xylan Endo-1,3-beta-Xylosidase