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The crystal structure of bovine lens γIIIb-crystallin at 2.5 Å resolution previously reported was interpreted using a consensus sequence derived from related vertebrate sequences on the assumption that γIIIb-crystallin derived from the γC-crystallin gene. It has recently been shown that γIIIb is a product of the bovine γD gene. The structure of γIIIb has now been refined with the bovine γD sequence using new 1.95 Å resolution synchrotron data. The crystallographic R factor was 20.4% for all 33 104 reflection data between 8.0 and 1.95 Å measured at 277(1) K. The electron density fully supported the assignment of the γD sequence to γIIIb. The crystal belongs to space group P212121 with two molecules of molecular mass 20 749 Da in the asymmetric unit in which 219 water molecules were located. The two-domain four-Greek-key motif highly symmetrical protein is very similar in structure to γB-crystallin (81% sequence identity). There is a single amino-acid deletion in γD in the linker region connecting the two domains. The intermolecular oganization in the crystal lattice is quite different from γB as a result of key mutations involving surface residues Leu51, Ile103 and His155. These point mutations will contribute to the intermolecular behaviour of the γ-crystallins in the eye lens, where they are major components of the densely packed, high refractive index regions of the lens.

Supporting information

PDB reference: 1elp

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