Structural perturbation of alpha-crystallin and its chaperone-like activity.
alpha-Crystallin is a multimeric lenticular protein that has recently been shown to be expressed in several non-lenticular tissues as well. It is shown to prevent aggregation of non-native proteins as a molecular chaperone. By using a non-thermal aggregation model, we could show that this process is temperature-dependent. We investigated the chaperone-like activity of alpha-crystallin towards photo-induced aggregation of gamma-crystallin, aggregation of insulin and on the refolding induced aggregation of beta- and gamma-crystallins. We observed that alpha-crystallin could prevent photo-aggregation of gamma-crystallin and this chaperone-like activity of alpha-crystallin is enhanced several fold at temperatures above 30 degrees C. This enhancement parallels the exposure of its hydrophobic surfaces as a function of temperature, probed using hydrophobic fluorescent probes such as pyrene and 8-anilinonaphthalene-1-sulfonate. We, therefore, concluded that alpha-crystallin prevents the aggregation of other proteins by providing appropriately placed hydrophobic surfaces; a structural transition above 30 degrees C involving enhanced or re-organized hydrophobic surfaces of alpha-crystallin is important for its chaperone-like activity. We also addressed the issue of conformational aspects of target proteins and found that their aggregation prone molten globule states bind to alpha-crystallin. We trace these developments and discuss some new lines that suggest the role of tertiary structural aspects in the chaperone process.
Rao
C M
CM
Centre for Cellular and Molecular Biology, Hyderabad, India. mohan@ccmb.ap.nic.in
Raman
B
B
Ramakrishna
T
T
Rajaraman
K
K
Ghosh
D
D
Datta
S
S
Trivedi
V D
VD
Sukhaswami
M B
MB
D000818:Animals; D003459:Crystallins / Q000737:chemistry* / Q000378:metabolism* / Q000528:radiation effects; D004229:Dithiothreitol; D066298:In Vitro Techniques; D007328:Insulin / Q000737:chemistry / Q000378:metabolism; D046911:Macromolecular Substances; D018832:Molecular Chaperones / Q000737:chemistry* / Q000378:metabolism* / Q000528:radiation effects; D010777:Photochemistry; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D013696:Temperature
D003459:Crystallins; D007328:Insulin; D046911:Macromolecular Substances; D018832:Molecular Chaperones; D004229:Dithiothreitol