Intrinsically disordered proteins (IDPs) do not autonomously adopt a stable unique 3D structure and exist as an ensemble ofrapidly interconverting structures. They are characterized by significant conformational plasticity and are associated withseveral biological functions and dysfunctions. The rapid conformational fluctuation is governed by the backbone segmentaldynamics arising due to the dihedral angle fluctuation on the Ramachandran ϕ–Ψ conformational space. We discovered thatthe intrinsic backbone torsional mobility can be monitored by a sensitive fluorescence readout, namely fluorescencedepolarization kinetics, of tryptophan in an archetypal IDP such as α-synuclein. This methodology allows us to map thesite-specific torsional mobility in the dihedral space within picosecond-nanosecond time range at a low protein concentrationunder the native condition. The characteristic timescale of * 1.4 ns, independent of residue position, representscollective torsional dynamics of dihedral angles (ϕ and Ψ) of several residues from tryptophan and is independent of overallglobal tumbling of the protein. We believe that fluorescence depolarization kinetics methodology will find broad applicationto study both short-range and long-range correlated motions, internal friction, binding-induced folding, disorder-to-ordertransition, misfolding and aggregation of IDPs.
Volume 48, 2023
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