Plastidic Phosphoglycerate Kinase from Phaeodactylum tricornutum: On the Critical Role of Cysteine Residues for the Enzyme Function

Regulation of photosynthetic carbon metabolism in aquatic and terrestrial organisms by Rubisco activase, redox-modulation and CP12

“…This study strongly suggested that the function of the pyrenoid might be controlled by light-driven reduction mediated by thioredoxins and photosystem-generated oxygen. In this diatom, PGA-kinase has also shown to be a target of thioredoxins (Bosco et al, 2012) but in general the C 3 cycle enzymes such as PRK and GAPDH are redox insensitive as in another marine diatom, T. pseudonana . Thus, it appears that in marine ecosystems, most redox regulation occurs at the carbon acquisition step rather than at the assimilation step.…”

Thioredoxin-dependent Redox Regulation of Chloroplastic Phosphoglycerate Kinase from Chlamydomonas reinhardtii

“…Similarly, PGKs from Synechocystis and P. tricornutum were found to be inactivated under oxidizing conditions through the formation of one or several disulfide bond(s) (23,24). However, whereas the Chlamydomonas enzyme resembles classical TRXregulated CBC enzymes from land plants activated under illumination, the Synechocystis enzyme is only inactivated in the presence of strong oxidants, suggesting that the CBC may be regulated by light in Chlamydomonas and by oxidants in cyanobacteria.…”

“…These results strongly suggest that PGK might contain redox-responsive cysteines probably located on the molecular surface of the enzyme. Recently, two reports demonstrated that PGK from the diatom Phaeodactylum tricornutum and the cyanobacteria Synechocystis are inactivated by oxidation and that the oxidized enzymes are reactivated by TRX (23,24). The redox sensitivity of both enzymes was proposed to involve oxidation to sulfenic acid of Cys 77 in P. tricornutum PGK and the formation of disulfide bonds between Cys 58 and Cys 95 and between Cys 314 and Cys 340 in PGK from P. tricornutum and Synechocystis, respectively.…”

Carbon Fixation in Diatoms

“…However, none of the several key enzymes in the Calvin cycle, which are under redox regulation in higher plants, appear to be regulated by Trxs in diatoms (Liaud et al 2000 ;Michels et al 2005 ;Kroth et al 2008 ;Weber et al 2009 ), with the so far only exception of the fructose-1,6-bisphosphatase (FBPase) and the phosphoglycerate kinase (Michels et al 2005 ;Bosco et al 2012 ). It is thus likely that the plastidic Trx systems in diatoms and in other chromist algae have undergone a unique functional specialization.…”