ИСТИНА

Molecular dynamics (MD) and quantum chemistry (QC) calculations allow to directly investigate the molecular mechanics of ultrafast charge separation reactions in Photosystem 1 (PS 1). A molecular model of PS I was developed with the aim to relate the atomic structure with electron transfer events in the two branches of cofactors. The MD model permits the study of atomic movements (dielectric polarization) in response to primary and secondary charge separations, while QC calculations allow to estimate the direct chemical effect of individual amino acids in the vicinity of the cofactors on the redox potential of these cofactors. QC were used to investigate the A0A/A0B ligands (Met in wild type or Asn of mutated version in the 688/668 position) on the redox potential of chlorophylls A0A/A0B and phylloquinones A1A/A1B. A combination of MD and semi-continual approaches was used to estimate reorganization energies λ of the primary (λ₁) and secondary (λ₂) charge separation reactions, which were found to be independent of the active branch of electron transfer. MD and QC approaches were used to describe the effect of substituting Met688(PsaA)/Met668(PsaB) by Asn688(PsaA)/Asn668(PsaB) on the energetics of electron transfer. The introduction of Asn and its conformation flexibility significantly affected the reorganization energy of charge separation and the redox potentials of chlorophylls A0A/A0B and phylloquinones A1A/A1B, introducing the new possible mechanism of electron transfer rate regulation. Obtained data was used to construct a kinetic model of the first steps of charge separation in PS 1, which portray the possibility of electron redistribution between chains A and B even after the primary charge separation.