Quantum Chemistry Calculations Provide Support to the Mechanism of the Light-Induced Structural Changes in the Flavin-Binding Photoreceptor Proteins

• DOI: 10.1021/ct100179p
• Publication Date: 2010-07-01T16:06:09Z
• Authors: M. G. Khrenova; A. V. Nemukhin; B. L. Grigorenko; A. I. Krylov; T. M. Domratcheva
• Keywords: Quantum Chemistry

The proposed mechanisms of photoinduced reactions in the blue light using flavin chromophore photoreceptor proteins are primarily based on results X-ray crystallography and spectroscopy studies. Of particular value observed band shifts optical vibrational spectra upon formation signaling (light-induced) state. However, same set experimental data has given rise to contradictory interpretations suggesting different structures dark states. To verify specific mechanism light-induced changes involving rotation/tautomerization transformations with conserved Gln residue near chromophore, we performed accurate quantum chemical calculations equilibrium structures, absorption bands model systems mimicking BLUF domain flavoprotein AppA. Geometry optimization frequencies were carried out QM(B3LYP/cc-pVDZ)/MM(AMBER) approach starting from representative molecular dynamics (MD) snapshots. MD simulations initiated available crystal AppA protein. Calculations vertical excitation energies scaled opposite spin configuration interaction single substitutions SOS-CIS(D) method that enables efficient treatment excited states large systems. computed as well spectral (the red shift by 12÷16 nm downshift 25 cm(-1) for C4═O mode) excellent agreement results, lending a strong support Domratcheva et al. (Biophys. J. 2008, 94, 3872).