Succinimide and isoaspartate residues in the crystal structures of hen egg-white lysozyme complexed with tri-N-acetylchitotriose

The isomerization of Asp101 to isoaspartate autocatalytically proceeds via a succinimide intermediate in hen egg-white lysozyme at a mildly acidic condition. The crystal structures of succinimide and isoaspartate forms of the lysozyme proteins, each complexed with a tri-N-acetylchito triose ligand, have been determined at 1.8 Angstrom resolution, and distinctively elucidate coplanar cyclic aminosuccinyl and beta-linked isoaspartyl residues. Compared with the liganded native protein with normal Asp101, succinimide 101 protrudes toward the ligand, and isoaspartate 101 extends away from the ligand. The formations of these residues caused the loss of three hydrogen-bonds between the ligand and the side-chains of Asp101 and Asn103 along with 0.5 Angstrom displacement of the ligand location. (C) 1998 Academic Press Limited.