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K.K. Sharma, J. Bhattacharyya; Mini alpha A-Crystallin and Mini alpha B-Crystallins: A Comparative Study . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2376.
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Purpose: To compare the molecular/structural properties of mini alpha A and mini-alpha B-crystallin chaperones (J. Biol. Chem. 275, 3767-3771, 2000 and Exp. Eye Res. 72, Suppl 2, 34, 2002), their mutants and retro forms. Methods: Mini-alpha A- (DFVIFLDVKHFSPEDLTVK) and mini-alpha B- (DRFSVNLDVKHFSPEELKVK) crystallin were synthesized and their chaperone-like activity was correlated with their CD spectra and interaction with bis-ANS. Chaperone-like activity of a series of Ala substituted mini-alpha A- peptides was determined using insulin aggregation assay and heat-induced ADH aggregation assay. Results: While the chaperone-like activity of mini-alpha A and mini alpha B- were comparable, mini-alpha B chaperone peptide displayed significantly lesser amount of beta sheet structure and lower bis-ANS binding compared to mini alpha A chaperone peptide. Heat treatment of mini alpha B at 70oC resulted in irreversible loss of beta sheet structure where as with mini-alpha A-crystallin the beta sheet structure was regained upon cooling of heat denatured peptide. Alpha B-retropeptide, though did not show beta sheet conformation showed chaperone-like activity whereas the retropeptide of mini-alpha A showed no chaperone-like activity or ellipticity during CD spectroscopy. Substitution of His in the peptide with Ala resulted in almost complete loss of chaperone-like activity in the case of mini alpha A- whereas only 40% decrease in the chaperone-like activity of mini alpha B- was observed with this substitution. Further, Ala scanning study with mini-alpha A showed that besides critical Phe residues, the acidic Asp and Glu are also essential for the activity of the peptide. Conclusion: Although mini-alpha A and mini-alpha B-crystallins have significant homology and both display chaperone-like activity they differ in hydrophobicity and structure. While the mini-alpha A is active in the beta sheet conformation the mini alpha B is active in both beta sheet and random conformation. Besides Phe His and acidic amino acids appear to play a role in the activity of mini alpha A activity.
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