  The photo-triggered unbinding of the intrinsically disordered S-peptide from
the RNase S complex is studied with the help of transient IR spectroscopy,
covering a wide range of time scales from 100 ps to 10 ms. To that end, an
azobenzene moiety has been linked to the S-peptide in a way that its helicity
is disrupted by light, thereby initiating its complete unbinding. The full
sequence of events is observed, starting from unfolding of the helical
structure of the S-peptide on a 20 ns timescale while still being in the
binding pocket of the S-protein, S-peptide unbinding after 300 microseconds,
and the structural response of the S-protein after 3 ms. With regard to the
S-peptide dynamics, the binding mechanism can be classified as an induced fit,
while the structural response of the S-protein is better described as
conformational selection.
