We are delighted to announce the generous support of our research group by the German Research Foundation (DFG). From 2023 to 2027, DFG FOR 5573 - GoPMF will investigate the dynamic regulation of the proton motive force (PMF) in photosynthesis.
The proton motive force (PMF) lies at the core of energy metabolism, fuelling a wide range of cellular processes. It is a universal phenomenon, comparable to the genetic code, and has played a significant role in shaping evolution. The PMF represents an electrochemical gradient across a membrane, typically generated by the coordinated activity of multiple membrane protein complexes. It serves to separate energy transformation from molecular identities and stoichiometric constraints, enabling the seamless integration of diverse cellular processes. This unique feature has been instrumental in the success of the PMF.
While the PMF exhibits remarkable flexibility, it must also maintain strict reliability to sustain cellular structures and fuel biochemical reactions. To ensure a constant energy supply under variable conditions, environmental and physiological stimuli need to be integrated into PMF regulation. Despite extensive research on the PMF, our understanding of its regulatory strategies remains incomplete.
Recent advancements in functional imaging and biosensing techniques have revealed new and fundamental insights into the mitochondrial PMF. These discoveries have begun to challenge our existing understanding of bioenergetic dynamics. However, similar insights are lacking for oxygenic photosynthesis. Studying the PMF within the context of photosynthesis is particularly suitable for understanding the underlying principles of its dynamics, as photosynthesis is highly susceptible to rapid external changes caused by fluctuating light in natural environments.
The goal of this Research Group (GoPMF) is to develop conceptual frameworks for understanding the regulation of PMF generation and modulation in order to optimize photosynthetic output in dynamic natural environments. Building upon recent discoveries and methodological advancements achieved by members of the research group, GoPMF investigates photosynthetic bioenergetics within the context of subcellular organization and physiology. GoPMF utilizes cyanobacteria and chloroplasts as in vivo models to dissect the regulatory mechanisms involved in rapid PMF adjustments at the posttranslational and physiological level. GoPMF complements these findings by mechanistic and structural analyses of the molecular machinery responsible for generating and modulating the PMF.
By combining cutting-edge imaging techniques with the development of in situ biosensing methods to monitor the bioenergetic characteristics of the PMF live in individual cells, organelles, and thylakoids, GoPMF aims to explore PMF management within a novel cell biological context. GoPMF gains molecular insights into the mechanisms driving PMF dynamics through fast time-resolved spectroscopy, mass spectrometry, and structural biology, including cryo-electron microscopy/tomography. Extensive genetic engineering approaches leverage the mechanistic conservation and diversity in PMF regulation found in cyanobacteria, algae, and plants. These functional studies are complemented by mathematical modelling of the PMF.
The ultimate goal of GoPMF is to establish a comprehensive understanding of the PMF as a dynamic, responsive, and integrated hub that shapes photosynthesis and enables its adaptation to rapid external changes.
GoPMF investigates the molecular mechanisms of electron transfer involving the cytochrome (Cyt) b6f complex (b6f), photosynthetic complex I and photosystem I (PSI) in vascular plants, green algae and cyanobacteria. Specifically, GoPMF explores how these cyclic electron transfer activities interact with the PMF and their relationship to photosynthetic H2 production in cyanobacteria.
The two components of the electrochemical gradient, ΔΨ and ΔpH, underlie a dynamic modulation by non-H+ ion fluxes such as K+, Ca2+ and Cl-. This modulation fine-tunes respiratory as well as photosynthetic electron transfer along with photoprotection. Complementary, ATP synthesis is dependent on the PMF and the responsiveness of the ATP synthase to the PMF is redox-controlled. GoPMF explores how the ATP synthase as well as ion channels and exchangers/carriers impact the local PMF and elucidates how PMF regulation relies on interdependent processes leading to a nonlinear complexity.
GoPMF advances innovative experimental approaches to explore PMF complexity and to reveal how PMF regulation underpins photosynthesis in vivo. The development and implementation of cutting-edge methodologies in the fields of biosensors, genetic manipulation and high resolution imaging are central to GoPMF. By utilizing genetically encoded biosensors of pH, transmembrane voltage, NAD(P)H and ATP, GoPMF establishes a connection between redox regulation, energy metabolism and PMF regulation. High resolution imaging techniques provide a foundation to investigate the PMF with unprecedented spatial and temporal resolution.
GoPMF determines the macromolecular organization of membrane proteins involved in PMF generation via cryogenic electron microscopy (cryo-EM) single particle analysis (SPA) and cryogenic electron tomography (cryo-ET) to elucidate how these structural scaffolds contribute to PMF regulation.
The redox state of NAD(P)+/NAD(P)H, quinones and thiol compounds along with the ATP/(ADP+AMP) energy status serve as key parameters to provide the cell with a dynamic readout of its current physiological state. In particular, the stromal NADPH/ATP ratio plays a critical role in connecting photosynthetic light reactions to carbon fixation. The PMF acts as a trigger for flexible adjustments of this ratio. In response to the cellular redox and energy status, posttranslational modifications such as phosphorylation and acetylation of thylakoid membrane proteins induce photoprotective mechanisms like energy-dependent (qE) and state transition-dependent (qT) non-photochemical quenching (NPQ). GoPMF investigates the components and dynamics of this regulatory network.