Comparing pigment arrangements in the many available structures of photosynthetic antenna complexes with those appearing in reaction centers, one notices that very similar arrangements of the same pigments have been chosen to function either as efficient light harvesters or as centers of ultrafast charge separation. It thus becomes obvious that the detailed pigment arrangement is not the main factor controlling excited state processes. Rather it is the surrounding protein that actually decides about the specific functioning in a particular case, i.e. whether a pigment cluster functions as an antenna or as a reaction center. Thus the protein � or more generally the �environment� - takes the role of a �smart responsive matrix�. At present we do not understand well the governing factors at a molecular level. However the design of efficient artificial antenna and charge separation units � with or without proteins � requires a deeper understanding and control of these environmental effects, i.e. the properties of the �responsive matrix�.  Recent studies on non-photochemical quenching (NPQ) in antenna complexes have turned out to provide fundamental insights into these environmental effects controlling the fate of the excited state energy. A common denominator of most NPQ quenching processes is the ultrafast formation of a chlorophyll-chlorophyll charge transfer state, by a mechanism that in many details operates in the same way as the �normal� processes of ultrafast photosynthetic charge separation occurring in reaction centers. Astounding and unexpected parallels between those - at first glance unrelated - processes of NPQ and of reaction center function have been found.  The talk will discuss the general principles governing the role of the surrounding protein in switching excitonically coupled pigment arrangements between light-harvesting, non-photochemical quenching, and energy-storing ultrafast charge separation in reaction centers.

From antennae to reaction centers and back: The key role of the protein as a responsive matrix in controlling excited state reactions

247th National Meeting (2014)

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