Energy Flow in the Cryptophyte PE545 Antenna Is Directed by Bilin Pigment Conformation

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• 作者：Carles Curutchet ; Vladimir I. Novoderezhkin ; Jacob Kongsted ; Aurora Mu帽oz-Losa ; Rienk van Grondelle ; Gregory D. Scholes ; Benedetta Mennucci
• 刊名：The Journal of Physical Chemistry B
• 出版年：2013
• 出版时间：April 25, 2013
• 年：2013
• 卷：117
• 期：16
• 页码：4263-4273
• 全文大小：599K
• 年卷期：v.117,no.16(April 25, 2013)
• ISSN：1520-5207

文摘

Structure-based calculations are combined with quantitative modeling of spectra and energy transfer dynamics to detemine the energy transfer scheme of the PE545 principal light-harvesting antenna of the cryptomonad Rhodomonas CS24. We use a recently developed quantum-mechanics/molecular mechanics (QM/MM) method that allows us to account for pigment鈥損rotein interactions at atomic detail in site energies, transition dipole moments, and electronic couplings. In addition, conformational flexibility of the pigment鈥損rotein complex is accounted for through molecular dynamics (MD) simulations. We find that conformational disorder largely smoothes the large energetic differences predicted from the crystal structure between the pseudosymmetric pairs PEB_50/61C鈥揚EB_50/61D and PEB_82C鈥揚EB_82D. Moreover, we find that, in contrast to chlorophyll-based photosynthetic complexes, pigment composition and conformation play a major role in defining the energy ladder in the PE545 complex, rather than specific pigment鈥損rotein interactions. This is explained by the remarkable conformational flexibility of the eight bilin pigments in PE545, characterized by a quasi-linear arrangement of four pyrrole units. The MD-QM/MM site energies allow us to reproduce the main features of the spectra, and minor adjustments of the energies of the three red-most pigments DBV_19A, DBV_19B, and PEB_82D allow us to model the spectra of PE545 with a similar quality compared to our original model (model E from Novoderezhkin et al. Biophys. J.2010, 99, 344), which was extracted from the spectral and kinetic fit. Moreover, the fit of the transient absorption kinetics is even better in the new structure-based model. The largest difference between our previous and present results is that the MD-QM/MM calculations predict a much smaller gap between the PEB_50/61C and PEB_50/61D sites, in better accord with chemical intuition. We conclude that the current adjusted MD-QM/MM energies are more reliable in order to explore the spectral properties and energy transfer dynamics in the PE545 complex.