Cytochrome b559 and cyclic electron transfer within photosystem II

Abstract

Cytochrome b₅₅₉ (Cyt b₅₅₉), β-carotene (Car), and chlorophyll (Chl) cofactors participate in the secondary electron-transfer pathways in photosystem II (PSII), which are believed to protect PSII from photodamage under conditions in which the primary electron-donation pathway leading to water oxidation is inhibited. Among these cofactors, Cyt b₅₅₉ is preferentially photooxidized under conditions in which the primary electron-donation pathway is blocked. When Cyt b₅₅₉ is preoxidized, the photooxidation of several of the 11 Car and 35 Chl molecules present per PSII is observed. In this review, the discovery of the secondary electron donors, their structures and electron-transfer properties, and progress in the characterization of the secondary electron-transfer pathways are discussed. This article is part of a Special Issue entitled: Photosystem II.

In vivo reconstitution of a homodimeric cytochrome b559 like structure: The role of the N-terminus α -subunit from Synechocystis sp. PCC 6803

“…For such a role, the Cyt b 559 has to change easily its redox state from reduced high potential to oxidized low potential forms. Such redox variability is actually observed experimentally in many different preparations of PSII and mutants Shinopoulos and Brudvig 2012;Guerrero et al 2013;Guerrero et al 2014, Sigiura et al 2015 though the underline molecular mechanisms for those changes are yet unknown.…”

“…The function of the Cyt b 559 is not well resolved yet but the most accepted hypothesis nowadays considers that it is involved in the photoinhibition/repair cycle of the PSII (Faller et al 2001;Alfonso et al 2004;Shinopoulos and Brudvig 2012;Guerrero et al 2014;Sugiura et al 2015). Accordingly, this cytochrome would accept electrons from an overreduced acceptor side (acceptor side photoinhibition) or deliver electrons to a deficient electron donor side (donor side photoinhibition) of the PSII.…”

“…Indeed, most of those cytochromes are made of a single polypeptide and their midpoint redox potentials (E m ) vary between -100 and +100 mV (Kaminskaya et al 1999;Roncel et al 2003;Shinopoulos and Brudvig 2012). However, the Cyt b 559 is a heterodimeric (α/β) protein (Nanba and Satoh 1987;Seibert and Picorel 2011) and it can reach an unusually high redox potential up to +400 mV that can widely vary depending on sample preparations and mutations (Kaminskaya et al 1999;Roncel et al 2003;Shinopoulos and Brudvig 2012;Ahmad et al 1993;Guerrero et al 2013;Guerrero et al 2014). These two properties make this metalloprotein more elusive and difficult to characterize, and establish its functional role.…”

“…Accordingly, this cytochrome would accept electrons from an overreduced acceptor side (acceptor side photoinhibition) or deliver electrons to a deficient electron donor side (donor side photoinhibition) of the PSII. The secondary plastoquinone (Q B ) is most probably the best candidate to donate electrons to the Cyt b 559 and the β-carotene of the D2 protein to accept electrons from the Cyt b 559 (Faller et al 2001;Shinopoulos and Brudvig 2012;Guerrero et al 2014;Sigiura et al 2015). Indeed, the heme moiety of this cytochrome is strategically located between the secondary Q B and the β-carotene in the crystal structure (Guskov et al 2009;Koua et al 2013).…”

Six amino acids define a minimal dimerization sequence and stabilize a transmembrane helix dimer by close packing and hydrogen bonding

“…In vivo, cytochrome b 559 is formed by the two single-span TM proteins PsbE and PsbF. In their TM region the two TM helices sandwich one heme molecule, which is non-covalently bound, resulting in formation of the holo-cytochrome [29]. Structurally, the TM region of cytochrome b 559 is divided into two parts: a heme-binding domain and a dimerization domain [30].…”