TY - JOUR
T1 - Dipole–dipole interactions between tryptophan side chains and hydration water molecules dominate the observed dynamic stokes shift of lysozyme
AU - Fukuda, Asahi
AU - Oroguchi, Tomotaka
AU - Nakasako, Masayoshi
N1 - Funding Information:
The MD simulation was conducted by using the supercomputer systems of the Research Center for Computational Science at the National Institutes of Natural Sciences , Okazaki, Japan. This study was supported by grants from the Japan Society for the Promotion of Science to M.N. (Nos. jp13480214 , jp19204042 , and jp22244054 ) and to T.O. (Nos. jp26800227 and jp17H04854 ) and grants from the Ministry of Education, Culture, Sports, Science and Technology to M.N. (Nos. jp15076210 , jp20050030 , jp22018027 , jp23120525 , jp25120725 , jp15H01647 , and jp17H05891 ) and T.O. (No. jp26104535 ).
Funding Information:
The MD simulation was conducted by using the supercomputer systems of the Research Center for Computational Science at the National Institutes of Natural Sciences, Okazaki, Japan. This study was supported by grants from the Japan Society for the Promotion of Science to M.N. (Nos. jp13480214, jp19204042, and jp22244054) and to T.O. (Nos. jp26800227 and jp17H04854) and grants from the Ministry of Education, Culture, Sports, Science and Technology to M.N. (Nos. jp15076210, jp20050030, jp22018027, jp23120525, jp25120725, jp15H01647, and jp17H05891) and T.O. (No. jp26104535).
PY - 2020/2
Y1 - 2020/2
N2 - The fluorescence intensity of tryptophan residues in hen egg-white lysozyme was measured up to 500 ps after the excitation by irradiation pulses at 290 nm. From the time-dependent variation of fluorescence intensity in a wavelength range of 320–370 nm, the energy relaxation in the dynamic Stokes shift was reconstructed as the temporal variation in wavenumber of the estimated fluorescence maximum. The relaxation was approximated by two exponential curves with decay constants of 1.2 and 26.7 ps. To interpret the relaxation, a molecular dynamics simulation of 75 ns was conducted for lysozyme immersed in a water box. From the simulation, the energy relaxation in the electrostatic interactions of each tryptophan residue was evaluated by using a scheme derived from the linear response theory. Dipole–dipole interactions between each of the Trp62 and Trp123 residues and hydration water molecules displayed an energy relaxation similar to that experimentally observed regarding time constants and magnitudes. The side chains of these residues were partly or fully exposed to the solvent. In addition, by inspecting the variation in dipole moments of the hydration water molecules around lysozyme, it was suggested that the observed relaxation could be attributed to the orientational relaxation of hydration water molecules participating in the hydrogen-bond network formed around each of the two tryptophan residues.
AB - The fluorescence intensity of tryptophan residues in hen egg-white lysozyme was measured up to 500 ps after the excitation by irradiation pulses at 290 nm. From the time-dependent variation of fluorescence intensity in a wavelength range of 320–370 nm, the energy relaxation in the dynamic Stokes shift was reconstructed as the temporal variation in wavenumber of the estimated fluorescence maximum. The relaxation was approximated by two exponential curves with decay constants of 1.2 and 26.7 ps. To interpret the relaxation, a molecular dynamics simulation of 75 ns was conducted for lysozyme immersed in a water box. From the simulation, the energy relaxation in the electrostatic interactions of each tryptophan residue was evaluated by using a scheme derived from the linear response theory. Dipole–dipole interactions between each of the Trp62 and Trp123 residues and hydration water molecules displayed an energy relaxation similar to that experimentally observed regarding time constants and magnitudes. The side chains of these residues were partly or fully exposed to the solvent. In addition, by inspecting the variation in dipole moments of the hydration water molecules around lysozyme, it was suggested that the observed relaxation could be attributed to the orientational relaxation of hydration water molecules participating in the hydrogen-bond network formed around each of the two tryptophan residues.
KW - Dipole–dipole interaction
KW - Dynamic stokes shift
KW - Energy relaxation
KW - Fluorescence of tryptophan
KW - Protein hydration
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U2 - 10.1016/j.bbagen.2019.07.015
DO - 10.1016/j.bbagen.2019.07.015
M3 - Article
C2 - 31377191
AN - SCOPUS:85070216761
VL - 1864
JO - Biochimica et Biophysica Acta - General Subjects
JF - Biochimica et Biophysica Acta - General Subjects
SN - 0006-3002
IS - 2
M1 - 129406
ER -