An evolutionary analysis of the reaction mechanisms of photosystem I reduction by cytochrome c6 and plastocyanin

Abstract

Photosystem I reduction by the soluble metalloproteins cytochrome c(6) and plastocyanin, which are alternatively synthesized by some photosynthetic organisms depending on the relative availability of copper and iron, has been investigated in cyanobacteria, green algae and plants. The reaction mechanism is classified in three different types on the basis of the affinity of the membrane complex towards its electron donor protein. The role of electrostatic interactions in forming an intermediate transient complex, as well as the structural and functional similarities of cytochrome c(6) and plastocyanin are analysed from an evolutionary point of view. The proposal made is that the heme protein was first "discovered" by nature, when iron was much more abundant on the Earth's surface, and replaced by plastocyanin when copper became available because of the oxidizing conditions of the new atmosphere.

Photosynthetic fuel for heterologous enzymes: the role of electron carrier proteins

“…PCC 6803 c 6 ) (Kerfeld and Krogmann 1998;Cho et al 1999;Howe et al 2006). While most cyanobacteria and green algae produce both plastocyanin and cytochrome c 6 (De La Rosa et al 2002), some cyanobacteria (such as Arthrospira platensis) use cytochrome c 6 instead of plastocyanin (Sandmann 1986). Like plastocyanin, cytochrome c 6 relies on electrostatic interactions for electron transfer, although the polarity of these can differ between plants and cyanobacteria (De La Rosa et al 2002).…”

Mutagenesis of Prochlorothrix Plastocyanin Reveals Additional Features in Photosystem I Interactions

“…Additionally, arginine at position 86 was replaced both by glutamine and glutamate ( Fig. 1), because an equivalent arginine has been shown to be crucial in the donor-PSI interaction in other cyanobacteria (5).…”

“…Mutations in Arg-86 -Cyanobacterial Pcs contain just one arginine residue (numbered Arg-88 in spinach) proposed to be crucial in PSI interaction because its substitution makes Anabaena Pc unable to reduce PSI (5,14). Mutating the equivalent Arg-86 in Prochlorothrix promotes a decrease in K A but to a lesser extent increases k et , the R86E mutant yielding a more pronounced effect.…”

“…However, the relevance of such electrostatic interactions in vivo can be different, as is the case for the interaction between cytochrome f and Pc (4). In cyanobacteria, site 2 can be either negatively or positively charged (5). All these differences between distinct organisms have led to different reaction mechanisms for PSI reduction (5)(6)(7).…”

“…In cyanobacteria, site 2 can be either negatively or positively charged (5). All these differences between distinct organisms have led to different reaction mechanisms for PSI reduction (5)(6)(7).…”