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Genomics and Applied Biology, 2010, Vol.1 No.2
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Figure 1 Multiple sequence alignments of
KR
homologs
Note: The three conserved residues of
A. hypogaea
KR corresponding to
E. coli
FabG Ser138, Tyr151 and Lys155 were highlighted
in asterisks; GenBank accession numbers were respectively as follows:
Arachis hypogaea
(FJ768728),
Glycine max
(ACU19360),
Arabidopsis thaliana
(NP_564216),
Ricinus communis
(AAA33873),
Synechocystis
PCC6803 (NP_440934),
Chlamydomonas
reinhardtii
(XP_001703473),
Escherichia coli
(AAC67304), and
Bacillus subtilis
(NP_389732)
spacing between the putative FabV active site tyrosine
and lysine residues was eight residues, two more than
FabI and FabL and one more than the maximum
reported for other SDR proteins. FabK, first
discovered in Streptococcus pneumoniae, was
refractory to triclosan and was a flavoprotein
unrelated to the SDR isozymes (Marrakchi et al.,
2003). The alignment of the predicted FabK-like
proteins from this subset of organisms demonstrated
that they possessed a conserved nucleotide-binding
domain in the N-terminus and a conserved
flavin-binding domain at the centre of the protein
(Figure 5B).
AhENR
and
AhKR
were members of the SDR
superfamily, and
AhENR
showed 16.1% sequence
identity with
AhKR
, compared with 25% in
Brassica
napus
(Fisher et al., 2000). However,
KR
and
ENR
catalyzed distinctly different chemical reactions,
namely a carbon–oxygen double-bond reduction and a
carbon–carbon double-bond reduction, respectively.
Fisher et al. (2000) reported that striking similarities
existed in fold, mechanism and substrate binding of
BnKR
and
BnENR
. Thus, these two enzymes may
have diverged from a common ancestor during the
evolution of the biosynthetic pathway. Phylogenetic
analysis suggested that the
AhENR
gene from peanut
formed a group with the genes from higher plants and
green algae, and set apart from the groups of
cyanobacteria and bacteria (Figure 6).