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In vivo heteromer formation. Expression of soluble βA4‐crystallin requires coexpression of a heteromeric partner
Author(s) -
MarínVinader Laura,
Onnekink Carla,
van Genesen Siebe T.,
Slingsby Christine,
Lubsen Nicolette H.
Publication year - 2006
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2006.05326.x
Subject(s) - crystallin , chaperone (clinical) , hsp70 , hsp27 , heat shock protein , microbiology and biotechnology , protein folding , co chaperone , biology , chemistry , biochemistry , biophysics , gene , medicine , pathology
The β‐crystallins are a family of long‐lived, abundant structural proteins that are coexpressed in the vertebrate lens. As β‐crystallins form heteromers, a process that involves transient exposure of hydrophobic interfaces, we have examined whether in vivo β‐crystallin assembly is enhanced by protein chaperones, either small heat shock proteins, Hsp27 or αB‐crystallin, or Hsp70. We show here that βA4‐crystallin is abundantly expressed in HeLa cells, but rapidly degraded, irrespective of the presence of Hsp27, αB‐crystallin or Hsp70. Degradation is even enhanced by Hsp70. Coexpression of βA4‐crystallin with βB2‐crystallin yielded abundant soluble βA4–βB2‐crystallin heteromers; βB1‐crystallin was much less effective in solubilizing βA4‐crystallin. As βB2‐crystallin competed for βA4‐crystallin with Hsp70 and the proteasomal degradation pathway, βB2‐crystallin probably captures an unstable βA4‐crystallin intermediate. We suggest that the proper folding of βA4‐crystallin is not mediated by general chaperones but requires a heteromeric partner, which then also acts as a dedicated chaperone towards βA4‐crystallin.