Site-selective dynamics of ligand-free and ligand-bound azidolysozyme

Azido-modified alanine residues (AlaN(3)) are environment-sensitive, minimally invasive infrared probes for the site-specific investigation of protein structure and dynamics. Here, the capability of the label is investigated to query whether or not a ligand is bound to the active site of lysozyme and how the spectroscopy and dynamics change upon ligand binding. The results demonstrate specific differences for center frequencies of the asymmetric azide stretch vibration, the longtime decay, and the static offset of the frequency fluctuation correlation function (FFCF)-all of which are experimental observables-between the ligand-free and the ligand-bound N-3-labeled protein. The center-frequency shifts range from 1 to 8 cm(-1), which is detectable from state-of-the art experiments. Similarly, the nonvanishing static component Delta(0) of the FFCF between ligand-free and ligand-bound protein can differ by up to a factor of 2.5. This makes the azide label a versatile and structurally sensitive probe to report on the dynamics of proteins in a variety of environments and for a range of different applications. Ligand-induced differences in the dynamics are also mapped onto changes in the local and through-space coupling between residues by virtue of dynamical cross correlation maps. This demonstrates that the position where the label is placed also influences the local and global protein motions.

Automated summary

Azido-modified alanine residues are environment-sensitive infrared probes for protein structure and dynamics. They can be used to investigate the binding of ligands to the active site of lysozyme and the changes in spectroscopy and dynamics upon ligand binding. The results show specific differences in center frequencies, longtime decay, and frequency fluctuation correlation function between the ligand-free and ligand-bound protein. This makes the azide label a versatile and structurally sensitive probe for studying protein dynamics.