The alternative splicing product αA ins-crystallin is structurally equivalent to αA and αB subunits in the rat α-crystallin aggregate

Abstract

In rodents and some other unrelated mammals, alternative splicing of the αA-crystallin gene transcript results in the synthesis of the elongated αA ins-crystallin chain. This polypeptide is identical to the normal αA-crystallin chain of 173 residues, but contains an additional sequence of 23 amino acid residues inserted between positions 63 and 64. To determine the effects of this insert peptide, the structure of the rat α-crystallin aggregate and its subunits αA-, αA insand αB-crystallin was studied using fluorescence spectra, partial urea dissociation, and lactoperoxidase-catalysed iodination of surface residues. The data suggest that all α-crystallin subunits occupy equivalent positions in the protein aggregate, and that the insert peptide merely elongates the connecting peptide between the putative amino- and carboxyl-terminal domain of the αA-crystallin subunit.