Frog lens βA1-crystallin: the nucleotide sequence of the cloned cDNA and computer graphics modelling of the three-dimensional structure

Four recombinant cDNA clones coding for a 23 kDa β-crystalline polypeptide of the frog (Rana temporariu) were identified in a collection of cloned cDNA and two of them were sequenced. The cDNA present in these clones codes for a polypeptide 198 amino-acid residues in length, which appears to be the frog βA1-crystallin because of its high homology with the sequences of βA1-crystallins from other species. Furthermore, the nucleotide sequence coding for the compact folded region of the protein is highly conserved. Virtually no homology was found in the 3′ nonstranslated regions of the mRNA. The amino-acid sequence of the Rana βA1-crystallin was used to build a three-dimensional model based on the coordinates of the homologous bovine γII. An analysis of the model shows that the surface residues of the βA1-crystallin (amphibian, mammalian and bird) are more highly conserved than the buried residues. It is suggested that this is related to the oligomeric nature of the lens β-crystallins