Many
deep eutectic solvents (DESs) are currently being explored
as environment-friendly media for biorelated applications. As an understanding
of the effect of these solvents on the structure of biomolecules is
crucial for these applications, we study how two DESs comprising trimethylglycine
(TMG) and ethylene glycol (EG) or glycerol (GL) influence the structural
stability and conformational dynamics of cytochrome c (Cytc) using
single-molecule-based fluorescence correlation spectroscopy (FCS)
technique and several other ensemble-based biophysical methods. The
FCS studies on A488-labeled Cytc enable an estimation of the size
(20.5 ± 1.5 Å) of the protein and capture its conformational
dynamics (54 ± 2 μs) in aqueous buffered solution. It is
observed that both size and conformational dynamics of the protein
are influenced in the presence of the DESs, but this effect is more
pronounced in the case of TMG-EG. The ensemble measurements on both
labeled and wild-type Cytc reveal that the protein structure is unfolded
completely by TMG-EG, whereas the structure is slightly altered by
TMG-GL. The results suggest that the behavior of Cytc in hydrated
DESs is determined by the strength of interactions between the DES
constituents as well as that between the constituents and the water
molecules present in the system.