A synthetic system mimics the Electron Transfer in Membranes: definition of the proteic scaffold

Cristina Cantale¹, Maria Stella Oriolo¹, Maria Sperandei¹, Maurizio Paci²

1 ENEA INN/BIOAG-BIMO Via Anguillarese, 301, 00060 S. Maria di Galeria Rome, Italy

2 Department of Chemistry, University "Tor Vergata", Via della Ricerca Scientifica, 00133 Rome, Italy

A great effort in the research world has been devoted to mimic the electron transfer of biological systems. The assembling of simplified proteic structures, molecular maquettes, with photosynthetic cofactors (chlorophylls, carotenoids, quinones) is considered a promising tool to gain relevant informations, allowing to study the main interactions, without the natural systems complexity.The pioneer works of DeGrado and coworkers (ranging from 1984-1995) have largely contributed in developping this approach, with a series of peptides binding up to four haem redox groups, which exhibit native-like properties in aqueous solution. We intend to carry out such an approach in simulated membrane systems (liposomes or Langmuir-Blodgett films). A de novo designed peptide was built, as the scaffold for a simple donor-acceptor system to be put inside a lipid film. A study of some wild protein structures in membranes was carried out, including structural motif as coiled coil and leucine zipper too, the signal peptides and the large complexes like the light harvesting and the photosynthetic reaction center, together with the statistics about the aminoacid propension in the different membrane portions. The designed peptide is 16 aminoacid long and it is planned to contain an hystidine as linker for the porphirine donor and it is covalently bound by its N-term portion to a loop system incorporating the acceptor, namely a substituted quinone. A simulation of the designed peptide using molecular modeling code GROMOS has been carried out, to gain confidence into the theoretical alphaelical structure. The peptide was synthesized by SPPS metodology, using Fastmoc, HBTU protocol. The product was evaluated by Mass Spectrometry and high-performance liquid chromatography (HPLC). Subsequently, it was purified to be used in NMR and CD experiments, to investigate the structure of this element of the whole maquette.

Keywords: Electron transfer, membrane, biological systems.