Plant Molecular Biology 40: 487–494, 1999.
© 1999 Kluwer Academic Publishers. Printed in the Netherlands.
Evidence for functional convergence of redox regulation in G6PDH
isoforms of cyanobacteria and higher plants
Urte K. Wendt
, Rüdiger Hauschild, Christian Lange
, Mario Pietersma, Irina Wenderoth
Antje von Schaewen
Pﬂanzenphysiologie, FB 5, Biologie/Chemie, Universität Osnabrück, 49069 Osnabrück, Germany (
MPB College GmbH, Eupener Str. 161, Eingang 60, 50933 Köln, Germany;
GenProﬁle AG, Robert-Roessle-Str. 10, 13125 Berlin, Germany
Received 5 October 1998; accepted in revised form 7 March 1999
Key words: cysteine positions, evolution, gene duplication, glucose-6-phosphate dehydrogenase, isoform classes,
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.
Glucose-6-phosphate 1-dehydrogenase (G6PDH, EC
18.104.22.168) catalyses the rate-limiting step of the oxida-
tive pentose phosphate pathway (OPPP). The OPPP
can be divided into an oxidative and a reversible
branch. Its main function is the generation of reducing
The nucleotide sequence data reported will appear in the
EMBL Database under the accession numbers: AJ001359 (Ara-
bidopsis thaliana plastidic clone APG1); AJ001769 and AJ001770
(Nicotiana tabacum cytosolic clones TCG6 and TCG9); AJ001771
and AJ001772 (Nicotiana tabacum plastidic clones TPG16 and
TPG18); AJ006246 (Galdieria sulphuraria plastidic clone Galdi-4);
AJ010712 (Solanum tuberosum plastidic clone P2); AJ010970
and AJ010971 (Arabidopsis thaliana cytosolic clones ACG9 and
ACG12); AJ132346 (Dunaliella bioculata plastidic clone Dun-5).
equivalentsand various sugar phosphatesfor reductive
biosynthesis (Copeland and Turner, 1987).
In higher plants, at least two G6PDH enzymes
exist in two different cellular compartments, i.e.
in the cytosol and in plastids. Both correspond-
ing genes are nuclear-encoded and share higher ho-
mology to each other (65%) than to cyanobacter-
ial homologues (about 55%) (von Schaewen et al.,
1995). A characteristic feature of cyanobacterial and
chloroplast G6PDH isoforms is inactivation by cova-
lent redox modiﬁcation mediated by the ferredoxin-
thioredoxin system (for recent reviews and a model,
see: Scheibe, 1990; Buchanan, 1991). This redox
chain ensures that speciﬁc target enzymes are ac-
tivated and kept in the reduced state in the light.