title: Highly controlled carbodiimide reaction for the modification of lysozyme. Modification of Leu129 or Asp119.
abstract: In the cross-linking reaction of lysozyme between Leu129 (alpha-COO-) and Lys13 (epsilon-NH3+) using imidazole and 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide hydrochloride (EDC), a side reaction of the peptide bond inversion from alpha to beta between Asp101 and Gly102 was greatly reduced by addition of beta-(1,4)-linked trimer of N-acetyl-D-glucosamine [(NAG)3]. When methylamine or 2-hydroxyethylamine was further added, the extent of the cross-link formation was decreased and the derivative where the alpha-carboxyl group of Leu129 was modified with the amine was newly obtained. On the other hand, when ammonia was added, the beta-carboxyl group of Asp119 instead of the alpha-carboxyl group was mainly amidated. From these results, the presence of a salt bridge between Asp119 and Arg125 besides that between Lys13 and Leu129, is proposed. Enzymatic activities of the derivatives prepared here indicated that the modification of the alpha-carboxyl group reduced the activity to approximately 90% of that of native lysozyme. Des-Leu129 lysozyme, which lacks Leu129, also showed approximately 90% of the activity of native lysozyme. Therefore, the salt bridge between Lys13 and Leu129 may play some role in maintaining the active conformation of lysozyme.
mesh_terms: D000595:Amino Acid Sequence; D001216:Asparagine; D003432:Cross-Linking Reagents; D005022:Ethyldimethylaminopropyl Carbodiimide; D007930:Leucine; D009113:Muramidase; D015202:Protein Engineering / Q000379:methods*
chemical_list: D003432:Cross-Linking Reagents; D001216:Asparagine; D009113:Muramidase; D007930:Leucine; D005022:Ethyldimethylaminopropyl Carbodiimide