Heat-induced conformational change and increased chaperone activity of lens alpha-crystallin.
OBJECTIVE
Alpha-crystallin is the major structural protein of the eye lens known to have chaperone-like activity. Our objective is to elucidate the nature of the thermal transition that alpha-crystallin undergoes at 60 degrees C and the effect of this transition on the chaperone activity.


METHODS
FPLC size exclusion chromatography, far- and near-ultraviolet circular dichroism, and tryptophan (Trp) and 1-anilino-8-naphthalenesulfonate (ANS) fluorescence were used to study conformational change. Turbidity of dithiothreitol (DTT)-reduced insulin was used to study chaperone activity.


RESULTS
The thermal transition was identified as a conformational change in mainly tertiary (partial unfolding) and quaternary high-molecular-weight (HMW) aggregation structures, along with a loss of 10 percentage points of secondary structure (beta-sheet). Initial partial perturbation in tertiary structure increased chaperone activity, but the increase was less in the HMW aggregate. Similar results were observed in in vivo-formed HMW alpha-crystallin.


CONCLUSIONS
The conformational change and HMW aggregation of alpha-crystallin observed at 60 degrees C, as well as in vivo-formed HMW aggregates, increased chaperone activity.
Das
B K
BK
Schepens Eye Research Institute, Harvard Medical School, Boston, MA, USA.
Liang
J J
JJ
Chakrabarti
B
B
D000817:Anilino Naphthalenesulfonates; D000818:Animals; D002417:Cattle; D002850:Chromatography, Gel; D002942:Circular Dichroism; D003459:Crystallins / Q000737:chemistry* / Q000378:metabolism*; D005260:Female; D005456:Fluorescent Dyes; D006358:Hot Temperature; D007908:Lens, Crystalline / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism*; D008968:Molecular Conformation
D000817:Anilino Naphthalenesulfonates; D003459:Crystallins; D005456:Fluorescent Dyes; D018832:Molecular Chaperones; C027132:1-anilino-8-naphthalenesulfonate