In vivo heteromer formation. Expression of soluble betaA4-crystallin requires coexpression of a heteromeric partner.
The beta-crystallins are a family of long-lived, abundant structural proteins that are coexpressed in the vertebrate lens. As beta-crystallins form heteromers, a process that involves transient exposure of hydrophobic interfaces, we have examined whether in vivobeta-crystallin assembly is enhanced by protein chaperones, either small heat shock proteins, Hsp27 or alphaB-crystallin, or Hsp70. We show here that betaA4-crystallin is abundantly expressed in HeLa cells, but rapidly degraded, irrespective of the presence of Hsp27, alphaB-crystallin or Hsp70. Degradation is even enhanced by Hsp70. Coexpression of betaA4-crystallin with betaB2-crystallin yielded abundant soluble betaA4-betaB2-crystallin heteromers; betaB1-crystallin was much less effective in solubilizing betaA4-crystallin. As betaB2-crystallin competed for betaA4-crystallin with Hsp70 and the proteasomal degradation pathway, betaB2-crystallin probably captures an unstable betaA4-crystallin intermediate. We suggest that the proper folding of betaA4-crystallin is not mediated by general chaperones but requires a heteromeric partner, which then also acts as a dedicated chaperone towards betaA4-crystallin.
Marín-Vinader
Laura
L
Department of Biochemistry, Radboud University Nijmegen, The Netherlands.
Onnekink
Carla
C
van Genesen
Siebe T
ST
Slingsby
Christine
C
Lubsen
Nicolette H
NH
D000818:Animals; D006224:Cricetinae; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D006367:HeLa Cells; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D007525:Isoelectric Focusing; D007976:Leupeptins / Q000494:pharmacology; D008156:Luciferases / Q000378:metabolism; D018832:Molecular Chaperones / Q000378:metabolism*; D009154:Mutation; D017510:Protein Folding; D012995:Solubility; D038205:beta-Crystallin A Chain / Q000235:genetics / Q000378:metabolism*; D038206:beta-Crystallin B Chain / Q000235:genetics / Q000378:metabolism; D038204:beta-Crystallins / Q000235:genetics / Q000378:metabolism
D004791:Enzyme Inhibitors; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D007976:Leupeptins; D018832:Molecular Chaperones; D038205:beta-Crystallin A Chain; D038206:beta-Crystallin B Chain; D038204:beta-Crystallins; C063261:acetylleucyl-leucyl-norleucinal; D008156:Luciferases; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde