Plastocyanin diffusion in the thylakoid lumen and its binding to cytochrome f (a subunit of the membrane b6f complex) were studied with a direct multiparticle simulation model that could also take account of their electrostatic interaction. Experimental data were used to estimate the model parameters for plastocyanin–cytochrome f complexing in solution. The model was then employed to assess the dependence of the association rate constant on the dimensions of the lumen. Highest rates were obtained at a lumen span of 8–10 nm; narrowing of the lumen below 7 nm resulted in drastic deceleration of complexing. This corresponded to the experimentally observed effect of hyperosmotic stress on the interaction between plastocyanin and cytochrome f in thylakoids.
Further developing the method for direct multiparticle modeling of electron transport in the thylakoid membrane, here we examine the influence of the shape of the reaction volume on the kinetics of the interaction of the mobile carrier with the membrane complex. Applied to cyclic electron transport around photosystem I, with account of the distribution of complexes in the membrane and restricted diffusion of the reactants, the model demonstrates that the biphasic character of the dark reduction of P700+ is quite naturally explained by the spatial heterogeneity of the system.
Most biological functions, including photosynthetic activity, are mediated by protein interactions. The proteins plastocyanin and cytochrome f are reaction partners in a photosynthetic electron transport chain. We designed a 3D computer simulation model of diffusion and interaction of spinach plastocyanin and turnip cytochrome f in solution. It is the first step in simulating the electron transfer from cytochrome f to photosystem 1 in the lumen of thylakoid. The model is multiparticle and it can describe the interaction of several hundreds of proteins. In our model the interacting proteins are represented as rigid bodies with spatial fixed charges. Translational and rotational motion of proteins is the result of the effect of stochastic Brownian force and electrostatic force. The Poisson–Boltzmann formalism is used to determine the electrostatic potential field generated around the proteins. Using this model we studied the kinetic characteristics of plastocyanin–cytochrome f complex formation for plastocyanin mutants at pH 7 and a variety of ionic strength values.
Electron spin resonance spectroscopy was used to monitor photoinduced changes in the redox state of P700, a photoactive pigment of phctosystemL in isolated Pisum sativum chloroplasts. The kinetics of the ESR signal from P700 (ESR signal I) was recorded at different concentrations of exogenous ferredoxin. A kinetic model was developed for ferredoxin-dependent cyclic electron transport around photosystem I. A multiparticle model was built to directly describe electron transfer in multienzyme complexes and restricted diffusion of mobile carriers in individual compartments (stroma, lumen, intramembrane space) of the system. The two models were compared, and a conclusion was made that the spatial organization of the system plays a significant role in shaping the kinetics of redox transitions of P700.
Работа посвящена разработке метода прямого компьютерного моделирования диффузии белков-подвижных переносчиков электрона и их взаимодействия с другими белками и белковыми комплексами в трехмерном пространстве. Метод является развитием метода прямого моделирования электронного транспорта в тилакоидной мембране, описанным ранее. Построена трехмерная компьютерная модель взаимодействия подвижного переносчика электрона белка пластоцианина с белком цитохромом f (одним из компонентов цитохромного комплекса) в растворе. Построенная модель позволила изучить влияние ионной силы на кинетические характеристики взаимодействия пластоцианина и цитохрома f.
В работе рассмотрены процессы взаимодействия подвижного переносчика пластоцианина с комплексом фотосистемы 1 и цитохромным комплексом. Построены прямая и кинетическая модели взаимодействия пластоцианина с ФС1 и cyt, оценены параметры прямой модели по экспериментальным данным. На кинетической модели исследовано влияние обратных реакций на характер кинетических кривых.
Построена многочастичная модель циклического Fd-зависимого электронного транспорта вокруг PSI, дающая возможность «прямого» моделирования процессов переноса электрона в мультиферментных комплексах и ограниченной диффузии подвижных переносчиков в отдельных компартментах системы (строма, люмен, внутримембранное пространство). Результаты прямого моделирования указывают на важную роль пространственной организации системы в формировании кинетики редокс-превращений P700.