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Abstract

In a recent paper (Wenderoth et al., J Biol Chem 272: 26985-26990, 1997) we reported that the positions of the two redox regulatory cysteines identified in a plastidic G6PD isoform from potato (Solanum tuberosum L.) differ substantially from those conserved in cyanobacterial G6PDH sequences. To investigate the origin of redox regulation in G6PDH enzymes from photoautotrophic organisms, we isolated and characterized several G6PD cDNA sequences from higher plants and from a green and a red alga. Alignments of the deduced amino acid sequences showed that the cysteine residues cluster in the coenzyme-binding domain of the plastidic isoforms and are conserved at three out of six positions. Comparison of the mature proteins and the signal peptides revealed that two different plastidic G6PDH classes (P1 and P2) evolved from a common ancestral gene. The two algal sequences branch off prior to this class separation in higher plants, sharing about similar amino acid identity with either of the two plastidic G6PDH classes. The genes for cytosolic plant isoforms clearly share a common ancestor with animal and fungal G6PDH homologues, whereas the cyanobacterial isoforms branch within the eubacterial G6PDH sequences. The data suggest that cysteine-mediated redox regulation arose independently in G6PDH isoenzymes of eubacterial and eukaryotic lineages.

A cytosolic glucose-6-phosphate dehydrogenase gene, ScG6PDH, plays a positive role in response to various abiotic stresses in sugarcane

“…In addition, two different types of plastidic G6PDH, P1 and P2, which evolved from a common ancestral gene, were discovered by researchers based on the alignment of mature proteins and signal peptides. The difference in signal peptides between P1 and P2 exists in the cleavage site, which is designated as (I/V/L)X(S/T/K)↓(S) for P1 and (I/V)X(S/T/A)↓(S/T/P/Q) for P2 7 . Furthermore, Wendt et al observed that the P1 and P2 isoforms showed different gene expression patterns in Solanum tuberosum L .…”

The Unique Cyanobacterial Protein OpcA Is an Allosteric Effector of Glucose-6-phosphate Dehydrogenase in Nostoc punctiformeATCC 29133

“…The inactivation of G6PD is mediated by thioredoxin (5,7,8,25) and occurs via covalent redox modification of specific regulatory cysteine residues (19). The location of the conserved cysteine residues differs between the cyanobacterial and chloroplast enzymes (19,26), and plants appear to lack any protein with similarity to cyanobacterial OpcA (BLAST search) (12), therefore, regulation of the two enzymes may be quite different. Because the oxidized and reduced forms of G6PD have been shown to differ in their affinities for G6P (19,23,27), we initially considered the possibility that strain UCD 351 G6PD and His-G6PD were in a reduced and inactive form and that the shift in apparent K m we observed was due to oxidative reactivation of the enzyme upon the addition of OpcA.…”

“…Because the activation of His-G6PD by His-OpcA occurred very rapidly, we could not distinguish between these two possibilities by catalytic assays. Like other cyanobacterial G6PDs, N. punctiforme G6PD contains cysteine residues in conserved positions that may be involved in redox modulation of enzyme activity (26). The N. punctiforme OpcA sequence also contains cysteine residues; of the nine present, those at positions 183, 195, 396, 401, and 407 are conserved in five other cyanobacterial sequences with homology to OpcA and therefore appear to be the most likely targets for thioredoxin-mediated redox modulation of OpcA activity, if it does occur.…”

Abscisic acid effects on activity and expression of barley (Hordeum vulgare) plastidial glucose-6-phosphate dehydrogenase

“…G6PDHs are tetrameric proteins formed by monomers of ∼50–60 kDa, which are present in all photosynthetic and non-photosynthetic organisms except the Archaea (Wendt et al , 1999). …”