TY - JOUR A1 - Morlock, Sascha A1 - Subramanian, Senthil Kumar A1 - Zouni, Athina A1 - Lisdat, Fred T1 - Closing the green gap of photosystem I with synthetic fluorophores for enhanced photocurrent generation in photobiocathodes JF - Chemical Science N2 - One restriction for biohybrid photovoltaics is the limited conversion of green light by most natural photoactive components. The present study aims to fill the green gap of photosystem I (PSI) with covalently linked fluorophores, ATTO 590 and ATTO 532. Photobiocathodes are prepared by combining a 20 μm thick 3D indium tin oxide (ITO) structure with these constructs to enhance the photocurrent density compared to setups based on native PSI. To this end, two electron transfer mechanisms, with and without a mediator, are studied to evaluate differences in the behavior of the constructs. Wavelength-dependent measurements confirm the influence of the additional fluorophores on the photocurrent. The performance is significantly increased for all modifications compared to native PSI when cytochrome c is present as a redox-mediator. The photocurrent almost doubles from −32.5 to up to −60.9 μA cm−2. For mediator-less photobiocathodes, interestingly, drastic differences appear between the constructs made with various dyes. While the turnover frequency (TOF) is doubled to 10 e−/PSI/s for PSI-ATTO590 on the 3D ITO compared to the reference specimen, the photocurrents are slightly smaller since the PSI-ATTO590 coverage is low. In contrast, the PSI-ATTO532 construct performs exceptionally well. The TOF increases to 31 e−/PSI/s, and a photocurrent of −47.0 μA cm−2 is obtained. This current is a factor of 6 better than the reference made with native PSI in direct electron transfer mode and sets a new record for mediator-free photobioelectrodes combining 3D electrode structures and light-converting biocomponents. Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-17022 VL - 14 SP - 1696 EP - 1708 PB - Royal Society of Chemistry (RSC) ER - TY - JOUR A1 - Morlock, Sascha A1 - Subramanian, Senthil Kumar A1 - Zouni, Athina A1 - Lisdat, Fred T1 - Bio-inorganic hybrid structures for direct electron transfer to photosystem I in photobioelectrodes JF - Biosensors and Bioelectronics N2 - Synthetic materials can be combined with biological components in many ways. One example that provides scientists with multiple challenges is a photobioelectrode that converts sunlight into electrons in a biohybrid approach. In the present study several key parameters are evaluated concerning their influence on the direct electron transfer from a 3D indium tin oxide (ITO) electrode material to photosystem I (PSI) as a light-harvesting biomolecule. In contrast to previous investigations, no mediating molecule is added to shuttle the electrons to the luminal side of PSI. Thus, this setup is less complex than foregoing ones. The solution composition drastically influences the interaction of PSI with the ITO surface. Here, the application of higher buffer concentrations and the addition of salts are advantageous, whereas the nature of the buffer ions plays a minor role. The artificial electrode material's thickness is adjustable since a spin-coating procedure is used for preparation. With a 30 μm thick structure and immobilized PSI cathodic photocurrents up to 10.1 μA cm−2 are obtained at 100 mW cm−2 illumination intensity and an applied potential of −0.1V vs. Ag/AgCl. Over a period of three days the photobioelectrodes are illuminated for a total of 90 min and stored between the measurements at ambient temperature. The stability of the setup is noteworthy as still about 90% of the photocurrent is retained. The photocathode described here offers many positive features, including a high onset potential for the photocurrent starting sligthly above the redox potentail of P700, and applicability in a wide pH range from pH 5 to 8. Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-16770 SN - 1873-4235 VL - 204 PB - Elsevier ER - TY - JOUR A1 - Morlock, Sascha A1 - Subramanian, Senthil Kumar A1 - Zouni, Athina A1 - Lisdat, Fred T1 - Scalable Three-Dimensional Photobioelectrodes Made of Reduced Graphene Oxide Combined with Photosystem I JF - ACS Applied Materials & Interfaces N2 - Photobioelectrodes represent one of the examples where artificial materials are combined with biological entities to undertake semi-artificial photosynthesis. Here, an approach is described that uses reduced graphene oxide (rGO) as an electrode material. This classical 2D material is used to construct a three-dimensional structure by a template-based approach combined with a simple spin-coating process during preparation. Inspired by this novel material and photosystem I (PSI), a biophotovoltaic electrode is being designed and investigated. Both direct electron transfer to PSI and mediated electron transfer via cytochrome c from horse heart as redox protein can be confirmed. Electrode preparation and protein immobilization have been optimized. The performance can be upscaled by adjusting the thickness of the 3D electrode using different numbers of spin-coating steps during preparation. Thus, photocurrents up to ∼14 μA/cm2 are measured for 12 spin-coated layers of rGO corresponding to a turnover frequency of 30 e– PSI–1 s–1 and external quantum efficiency (EQE) of 0.07% at a thickness of about 15 μm. Operational stability has been analyzed for several days. Particularly, the performance at low illumination intensities is very promising (1.39 μA/cm2 at 0.1 mW/cm2 and −0.15 V vs Ag/AgCl; EQE 6.8%). KW - biophotovoltaics KW - reduced graphene oxide (rGO) KW - scalable template process KW - spin-coating KW - 3D electrode structure KW - carbon material Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-16760 VL - 13 IS - 9 SP - 11237 EP - 11246 PB - American Chemical Society (ACS) ER - TY - JOUR A1 - Kölsch, Adrian A1 - Radon, C. A1 - Golub, M. A1 - Baumert, A. A1 - Bürger, Jörg A1 - Mielke, Thorsten A1 - Lisdat, Fred A1 - Feoktystov, Artem A1 - Pieper, Jörg A1 - Zouni, Athina A1 - Wendler, Petra T1 - Current limits of structural biology: The transient interaction between cytochrome c6 and photosystem I JF - Current Research in Structural Biology N2 - Trimeric photosystem I from the cyanobacterium Thermosynechococcus elongatus (TePSI) is an intrinsic membrane protein, which converts solar energy into electrical energy by oxidizing the soluble redox mediator cytochrome c6 (Cyt c6) and reducing ferredoxin. Here, we use cryo-electron microscopy and small angle neutron scattering (SANS) to characterize the transient binding of Cyt c6 to TePSI. The structure of TePSI cross-linked to Cyt c6 was solved at a resolution of 2.9 Å and shows additional cofactors as well as side chain density for 84% of the peptide chain of subunit PsaK, revealing a hydrophobic, membrane intrinsic loop that enables binding of associated proteins. Due to the poor binding specificity, Cyt c6 could not be localized with certainty in our cryo-EM analysis. SANS measurements confirm that Cyt c6 does not bind to TePSI at protein concentrations comparable to those for cross-linking. However, SANS data indicate a complex formation between TePSI and the non-native mitochondrial cytochrome from horse heart (Cyt cHH). Our study pinpoints the difficulty of identifying very small binding partners (less than 5% of the overall size) in EM structures when binding affinities are poor. We relate our results to well resolved co-structures with known binding affinities and recommend confirmatory methods for complexes with KM values higher than 20 μM. KW - photosystem I KW - cryo-EM KW - Thermosynechococcus elongatus KW - small angle neutron scattering KW - cytochrome c6 KW - electron transfer KW - photo-biotechnology Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-13628 SN - 2665-928X VL - 2 SP - 171 EP - 179 ER - TY - GEN A1 - Stieger, Kai Ralf A1 - Feifel, Sven Christian A1 - Lokstein, Heiko A1 - Hejazi, Mahdi A1 - Zouni, Athina A1 - Lisdat, Fred T1 - Biohybride Architekturen für eine effiziente Umwandlung von Licht in elektrische Energie durch Integration von Photosystem I in skalierbare mesoporöse 3D Elektroden T2 - Wissenschaftliche Beiträge 2018 N2 - Die Kombination von fortschrittlichen Materialien und kontrolliertem Oberflächendesign mit komplexen Proteinen aus der natürlichen Photosynthese ist derzeit eines der Hauptthemen bei der Entwicklung von Biohybridsystemen und Biophotovoltaik. In dieser Studie werden transparente makroporöse Indium-Zinn-Oxid-(μITO-) Elektroden mit dem trimeren Superkomplex Photosystem I (PSI) aus dem Cyanobakterium Thermosynechococcus elongatus sowie dem kleinen Redoxprotein Cytochrom c (Cyt c) kombiniert, um neuartige und effiziente biohybride Photokathoden herzustellen. Mit diesen bis zu 40 μm hohen 3D-Strukturen können beide Proteine in einer annähernden Monolage abgeschieden werden und die elektrische Kommunikation mit der Elektrode kann erzielt werden. Der generierte Photostrom folgt dabei linear der kontrollierbaren Schichtdicke der μITO-Elektrode, wobei Stromdichten von bis zu 150 μA cm –2 erhalten werden. Eine effiziente elektrische Kopplung der Proteine kann durch die hohe interne Quanteneffizienz von 30 % gezeigt werden. N2 - The combination of advanced materials and a controlled surface design with complex proteins from natural photosynthesis is currently one of the major topics in the development of biohybrid systems and biophotovoltaic devices. In this study, transparent macroporous indium tin oxide (μITO) electrodes are combined with the trimeric supercomplex, Photosystem I (PSI) from the cyanobacterium Thermosynechococcus elongatus, and the small redox protein cytochrome c (cyt c) to create novel and efficient biohybrid photocathodes. With these 3D structures up to 40 μm in size, both proteins can be deposited in a monolayer fashion and electrical communication with the electrode can be established. The generated photocurrent linearly follows the controllable layer thickness of the μITO electrode up to 40 μm, whereby current densities of up to 150 μA cm –2 are obtained. An efficient electrical coupling of the proteins can be demonstrated by the high internal quantum efficiency of 30 %. Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-10220 SN - 0949-8214 VL - 22 SP - 17 EP - 24 ER - TY - JOUR A1 - Kölsch, Adrian A1 - Hejazi, Mahdi A1 - Stieger, Kai Ralf A1 - Feifel, Sven Christian A1 - Kern, Jan F. A1 - Müh, Frank A1 - Lisdat, Fred A1 - Lokstein, Heiko A1 - Zouni, Athina T1 - Insights into the binding behavior of native and non-native cytochromes to photosystem I from Thermosynechococcus elongatus JF - Journal of Biological Chemistry N2 - The binding of photosystem I (PS I) from Thermosynechococcus elongatus to the native cytochrome (cyt) c6 and cyt c from horse heart (cyt cHH) was analyzed by oxygen consumption measurements, isothermal titration calorimetry (ITC), and rigid body docking combined with electrostatic computations of binding energies. Although PS I has a higher affinity for cyt cHH than for cyt c6, the influence of ionic strength and pH on binding is different in the two cases. ITC and theoretical computations revealed the existence of unspecific binding sites for cyt cHH besides one specific binding site close to P700. Binding to PS I was found to be the same for reduced and oxidized cyt cHH. Based on this information, suitable conditions for cocrystallization of cyt cHH with PS I were found, resulting in crystals with a PS I:cyt cHH ratio of 1:1. A crystal structure at 3.4-Å resolution was obtained, but cyt cHH cannot be identified in the electron density map because of unspecific binding sites and/or high flexibility at the specific binding site. Modeling the binding of cyt c6 to PS I revealed a specific binding site where the distance and orientation of cyt c6 relative to P700 are comparable with cyt c2 from purple bacteria relative to P870. This work provides new insights into the binding modes of different cytochromes to PS I, thus facilitating steps toward solving the PS I–cyt c costructure and a more detailed understanding of natural electron transport processes. Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-12780 SN - 1083-351X VL - 293 IS - 23 SP - 9090 EP - 9100 ER -