Figure 1. The structures of αA- and αB-crystallins. A: Primary and secondary structures of αA- and αB-crystallins [13]. The secondary structure is denoted by upper letters; β, α, L and T indicate strands, helices, loops and COOH-terminal tail, respectively. Regions for which structural information is available in bovine αA-crystallin (PDB ID: 3L1E) and human αB-crystallin (PDB ID: 3L1G) are underlined [13]. The letters in boxes indicate aspartyl residues in which digestion by Asp-N occurs, and those on an orange background indicate isomerizable residues in human αA- and αB-crystallins. B: Tertiary structures of αA- (left) and αB- (right) crystallins. Numbers indicate the amino acid positions. The dashed lines indicate disordered regions. The letters in boxes indicate aspartyl residues in which digestion by Asp-N occurs, and those on an orange background indicate isomerizable residues in αA-crystallin and in αB-crystallin in vivo. Asp151 in αA-crystallin, and Asp73, Asp140 and Asn146 in αB-crystallin noted in the text are drawn in ball-and-stick models to make clear their positions. The figures were drawn by MOLSCRIPT [23] and RASTER3D [24]. Left: The recombinant bovine αA-crystallins (cyan, PDB ID: 3L1E). The β strands 2, 3, 8 and 9, the hinge loop region noted in the text (Gln147 - Ala155) and the C-terminal tail of the other bovine αA-crystallin crystal structure (black, PDB ID: 3L1F) are superposed [13]. The hinge loop region is colored in magenta in 3L1E. Right: One of the crystal structures of recombinant human αB-crystallins (pink, PDB ID: 3L1G). The β strands 3, 8 and 9 and available NH₂-terminal region of the representative model in NMR structure (black, molecule A in model 1 in PDB ID: 2KLR) are superposed [13,15].