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Protein dynamics control proton transfer from bulk solvent to protein interior: A case study with a green fluorescent protein
Author(s) -
Saxena Anoop M.,
Udgaonkar Jayant B.,
Krishnamoorthy Guruswamy
Publication year - 2005
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1110/ps.051391205
Subject(s) - chemistry , proton , kinetics , green fluorescent protein , fluorescence , flash photolysis , viscosity , protein dynamics , solvent , biophysics , photochemistry , protein structure , reaction rate constant , thermodynamics , biochemistry , physics , quantum mechanics , biology , gene
Abstract The kinetics of proton transfer in Green Fluorescent Protein (GFP) have been studied as a model system for characterizing the correlation between dynamics and function of proteins in general. The kinetics in EGFP (a variant of GFP) were monitored by using a laser‐induced pH jump method. The pH was jumped from 8 to 5 by nanosecond flash photolysis of the “caged proton,” o ‐nitrobenzaldehyde, and subsequent proton transfer was monitored by following the decrease in fluorescence intensity. The modulation of proton transfer kinetics by external perturbants such as viscosity, pH, and subdenaturing concentrations of GdnHCl as well as of salts was studied. The rate of proton transfer was inversely proportional to solvent viscosity, suggesting that the rate‐limiting step is the transfer of protons through the protein matrix. The rate is accelerated at lower pH values, and measurements of the fluorescence properties of tryptophan 57 suggest that the enhancement in rate is associated with an enhancement in protein dynamics. The rate of proton transfer is nearly independent of temperature, unlike the rate of the reverse process. When the stability of the protein was either decreased or increased by the addition of co‐solutes, including the salts KCl, KNO 3 , and K 2 SO 4 , a significant decrease in the rate of proton transfer was observed in all cases. The lack of correlation between the rate of proton transfer and the stability of the protein suggests that the structure is tuned to ensure maximum efficiency of the dynamics that control the proton transfer function of the protein.