Steady-state and time-resolved fluorescence studies on the ligand-induced conformational change in an active lysozyme derivative, Kyn62-lysozyme

The ligand-induced conformational change of an active lysozyme derivative, Kyn62-lysozyme, in which Trp62 of hen egg-white lysozyme (EC 3.2.1.17) was selectively modified to kynurenine, was investigated by steady-state and time-resolved fluorescence spectroscopy. Kyn62 formed an intramolecular energy transfer donor-acceptor pair with a tryptophan residue as a donor. The energy transfer was related to the conformation of the active site. The spectral overlap integral (J) of the kynurenine-tryptophan pair is large as it was determined to be 4.92 x 10^-15 M^-1 cm³. Time-resolved fluorescence properties of Kyn62-lysozyme and its complex with a trimer of N- acetyl-D-glucosamine [(GlcNAc)₃] show that the energy donor is Trp28 or Trp111 in the hydrophobic matrix box of the free Kyn62-lysozyme. In the complex, it appears that the kynurenine residue drastically changed its orientation or approached closer to Trp108 to accept more efficiently the excitation energy from Trp108 on the binding of Kyn62-lysozyme with (GlcNAc)₃.