The internal motion of lysozyme was described by the steady-state and time-resolved fluorescence anisotropy of its tryptophan residues. The fluorescence of mutant lysozymes W62Y- and W108Y-lysozyme, in which Trp62 or Trp108 of hen egg white lysozyme was replaced with a tyrosine residue, could be respectively assigned to Trp108 or Trp62 at the longer wavelength region of the total fluorescence spectrum. The segmental motion of Trp62 as shown by its fluorescence anisotropy decay was described with two components originating from the fluctuational rotation of an indole moiety about the Calpha-Cbeta bond and rotational wobble of the peptide segment adjacent to Trp62. Although Trp62 showed a high degree of motional freedom, its motion was significantly suppressed by the interaction of the mutant protein with a trimer of N-acetyl-D-glucosamine. By contrast, the segmental motion of Trp108 is hindered by the local cage structure at temperatures below 30 degreesC, but Relief from restricted motion occurred on the formation of ligand complex or by thermal agitation. Because of overlaps of the fluorescence spectrum, it is difficult to assign the segmental motion of Trp28 or Trp111, the other two tryptophan residues in lysozyme. However, a careful analysis of the fluorescence anisotropy decay of W62Y- and W108Y-lysozyme showed that the fluctuation of the hydrophobic matrix box was greater than that expected from lysozyme's crystal structure, although it was suppressed by the binding of the ligand to the active site of lysozyme.

No abstract

Tachyplesin I, an antibacterial and antiviral heptadecapeptide from the hemocyte debris of Tachypleus tridentatus, contains four aromatic amino acids (Trp2, Phe4, Tyr8, and Tyr13) which have been shown to be crucial for activity. In order to investigate conformations and orientations of the aromatic amino acid residues of tachyplesin I in lipid bilayers, its analogs, [Phe8]- and/or [Phe13]-tachyplesin(s) I in which Tyr8 and Tyr13 are replaced by Phe, were synthesized. Circular dichroism spectral studies showed that three peptides are considerably different in conformation in aqueous solution at pH 8.0 whereas they take similar conformations in the presence of neutral egg yolk phosphatidylcholine (EYPC) liposomes. Energy transfer kinetics showed that the distances of Trp2-Tyr8 and Trp2-Tyr13 are 16 A (max of 18.3 A, min of 15.1 A) and 18 A (max of 20.2 A, min of 16.6 A) in buffer but are 12 A (max of 15.2 A, min of 8.6 A) and 18 A (max of 22.9 A, min of 12.9 A), respectively, in the presence of acidic EYPC/EYPG (3:1) liposomes. Decay kinetics for Trp2 fluorescence indicated that Trp2 takes at least three conformations in buffer and in acidic liposomes where fractions of three Trp2 conformers vary by changing the medium from buffer to acidic liposomes. Although tachyplesin I is not in amphiphilic structure in buffer in spite of its rigid antiparallel beta-conformation, its interaction with lipid bilayers appears to induce amphiphilic structure via minor alteration of peptide backbone and side chain orientations, resulting in shortening the distance of Trp2-Tyr8.

No abstract