Crystallographic analysis of the photosynthetic reaction center from Rhodobacter sphaeroides bioconjugated with an artif
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MRS Advances © 2016 Materials Research Society DOI: 10.1557/adv.2016.10
Crystallographic analysis of the photosynthetic reaction center from Rhodobacter sphaeroides bioconjugated with an artificial antenna Benny Danilo Belviso1,§, Rocco Roberto Tangorra2,#, Francesco Milano3, Omar Hassan Omar4, Simona la Gatta2, Roberta Ragni2, Angela Agostiano2,3, Gianluca M. Farinola2, Rocco Caliandro1,*, Massimo Trotta3,* 1
Istituto di Cristallografia – Consiglio Nazionale delle Ricerche Via Amendola 122/o, 70125 Bari, Italy 2 Dipartimento di Chimica, Università degli Studi di Bari “Aldo Moro” Via Orabona 4, 70125 Bari, Italy 3 Istituto per i Processi Chimico Fisici, Consiglio Nazionale delle Ricerche Via Orabona 4, 70125 Bari, Italy 4 Istituto di Chimica dei Composti Organometallici, Consiglio Nazionale delle Ricerche Via Orabona 4, 70125 Bari, Italy §
Present address: Centre for Biomolecular Science, University of Nottingham, University Park Nottingham, NG7 2RD, UK # Present address: Mossi & Ghisolfi Group, Strada Ribrocca 11, 15057 Tortona (AL), Italy *[email protected], [email protected]. ABSTRACT A high-throughput crystallographic investigation on several crystals of photosynthetic reaction center covalently bound to an ad-hoc synthesized artificial antenna (AE600) is presented. The investigation did not show a preferential binding site of the antenna molecule AE600 to the reaction center in the solid phase. An accurate crystallographic study allowed identifying a lysine residue sitting on periplasmic side of the protein as one of the bioconjugation sites. The residue sits on subunit M of the protein, in close proximity to the bacteriochlorophylls of the reaction center involved in the light absorption and conversion processes. Distances obtained from the crystallographic structure confirm that energy transfer between the antenna and the protein proceed with the Förster resonance mechanism. INTRODUCTION Biomimetic systems mimicking the main functions of a natural photosynthetic apparatus require the presence of a functional unit able to collect solar energy and, as an antenna would do, drive it to a photochemical core to convert it in other energy forms. Natural systems, i.e. plants, algae, and photosynthetic bacteria perform this task in pigment-protein complexes, functioning as antenna, which collect and transfer energy to the protein photosynthetic reaction center (RC) operating as photoconverter1. The RC of the photosynthetic bacterium Rhodobacter (R.) sphaeroides can be assembled with organic fluorophores in fully functional covalent complexes capable of absorbing light and efficiently performing photo-conversion2-4. Here, we present an X-ray structural investigation on several crystals of RC covalently bound to the artificial antenna AE600. This fluorophore was
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