Interaction of α-lactalbumin with mini-αA-crystallin

Abstract

αA-Crystallin can function like a molecular chaperone. We have recently shown that residues 71-88 in αA-crystallin represent the "chaperone active site" of the protein. A peptide containing the sequence of αA-crystallin sequence DFVIFLDVKHFSPEDLTVK (mini αA-crystallin) by itself displays the antiaggregation property of αA-crystallin. We have prepared a complex of reduced α-lactalbumin and mini-αA-crystallin and investigated the nature, conformation, and properties of the complex by dynamic light scattering, HPLC analysis, CD spectroscopy, and fluorescence studies. Although mini-αA was able to prevent the precipitation of reduced α-lactalbumin, large aggregates (50-500 nm) of the complex were formed during the assay. Amino acid composition estimation revealed that α-lactalbumin and mini-αA-crystallin were present in 1:2 ratio in the aggregates. During our study significant red shift in the Trp fluorescence emission maximum and an increase in Bis-ANS binding to the mini αA-crystallin-bound α-lacatalbumin were observed. The CD spectra of the complex showed a significant loss of α-helical content but the β-sheet content appeared to be less affected, indicating the molten-globule state of the reduced lactalbumin in the complex. These data show that the active site of αA-crystallin by itself can maintain a significantly denatured and unfolded protein in soluble form.