Function and organization of Photosystem I polypeptides

Abstract

Photosystem I functions as a plastocyanin:ferredoxin oxidoreductase in the thylakoid membranes of chloroplasts and cyanobacteria. The PS I complex contains the photosynthetic pigments, the reaction center P700, and five electron transfer centers (A0, A1, FX, FA, and FB) that are bound to the PsaA, PsaB, and PsaC proteins. In addition, PS I complex contains at least eight other polypeptides that are accessory in their functions. Recent use of cyanobacterial molecular genetics has revealed functions of the accessory subunits of PS I. Site-directed mutagenesis is now being used to explore structure-function relations in PS I. The overall architecture of PSI complex has been revealed by X-ray crystallography, electron microscopy, and biochemical methods. The information obtained by different techniques can be used to propose a model for the organization of PS I. Spectroscopic and molecular genetic techniques have deciphered interaction of PS I proteins with the soluble electron transfer partners. This review focuses on the recent structural, biochemical and molecular genetic studies that decipher topology and functions of PS I proteins, and their interactions with soluble electron carriers.

Photosystem I, an Improved Model of the Stromal Subunits PsaC, PsaD, and PsaE

“…When the same reaction is conducted at pH 9.8, a pH where amino groups with an alkaline-shifted pK are more likely to react, the N-terminal Ala 1 and all ⑀-amino groups of lysines become labeled, except that of Lys 11 , suggesting that Lys 11 could be interacting with the PSI core. 2 This observation is in agreement with our structural model, since Lys 11 of PsaE from Synechocystis PCC6803 corresponds to the C-terminal residue of the loop AB, which is located close to the loop j-k of PsaA or PsaB. Recent biochemical studies on PSI complexes from Synechocystis sp.…”

The Unique Proline of the Prochlorothrix hollandica Plastocyanin Hydrophobic Patch Impairs Electron Transfer to Photosystem I

“…1 is a small redox protein (molecular mass, ϳ10.5 kDa) that functions in photosynthesis as a mobile electron carrier between the two membrane-embedded complexes cytochrome b 6 f and photosystem I (PSI) (1)(2)(3). Whereas higher plants produce just Pc, there is a number of intermediate species, both cyanobacteria and eukaryotic algae, that are able to synthesize cytochrome c 6 as an alternative redox carrier under copper deficiency (4).…”

Topography of the Photosystem I Core Proteins of the Cyanobacterium Synechocystis sp. PCC 6803

“…1 from cyanobacteria and chloroplasts is a multisubunit membrane-protein complex that catalyzes electron transfer from reduced plastocyanin (or cytochrome c 6 ) to oxidized ferredoxin (or flavodoxin) (1)(2)(3)(4). The PsaA and PsaB subunits of PS I form the heterodimeric core of the complex which harbors approximately 100 antenna chlorophyll a molecules, 10 -12 ␤-carotenes, the primary electron donor P700, and a chain of electron acceptors (A 0 , A 1 , and F X ).…”

“…PsaA and PsaB also interact directly with plastocyanin or cytochrome c 6 (5)(6)(7). In addition to the core proteins, the cyanobacterial PS I complex contains 9 small subunits (1)(2)(3). PsaC binds the terminal electron acceptors F A and F B , which are two [4Fe-4S] center (8).…”

“…Therefore, the N terminus of PsaA was exposed to proteases in the osmotically shocked cells showing that it is on the n side of photosynthetic membranes. DISCUSSION PS I is a multisubunit protein complex that contains at least 11 polypeptides in cyanobacteria (1). In this study, we used domain-specific antibodies, limited proteolysis, and subunitdeficient PS I complexes to understand the topography of the PsaA and PsaB proteins that form the catalytic hydrophobic core of PS I. Domain-specific antibodies were generated against specific peptides in PsaA and PsaB.…”