Advanced EPR characterization of photosynthetic Cytochrome c550

Abstract

Here Cytochrome c550 (Cc550) is a c-type heme protein with a bis-histidinyl axial coordination adscribed as an extrinsic component in the luminal side of photosys-tem II (PSII), although its role within this complex is not yet well established. Cc550 is present in cyanobacteria as well as in eukaryotic algae from the red photosynthetic lineage, which includes diatoms. However, the protein is absent in the green lineage, which comprises green algae and plants. In this contribution, we show the characterization by means of EPR techniques of two Cc550 from different Kingdoms, Cc550 from the diatom Phaeodactylum tricornu-tum and Cc550 from the cyanobactierum Synechocystis. This includes CW-EPR and ESEEM (HYSCORE) techniques, both at X-band and Q-band. Experimental results are compared and discussed on the basis of structural and functional similarities and differences of both proteins. This study shows how ad-vances EPR characterization is a powerful tool for revealing structural details in hemeproteins.