|Characterization of shikimate dehydrogenase homologues of Corynebacterium glutamicum.
Appl. Microbiol. Biotechnol. 97: 8139-8149. 2013.
T. Kubota, Y. Tanaka, K. Hiraga, M. Inui and H. Yukawa.
|The function of three Corynebacterium glutamicum shikimate dehydrogenase homologues, designated as qsuD (cgR_0495), cgR_1216,
and aroE (cgR_1677), was investigated. A disruptant of aroE required shikimate
for growth, whereas a qsuD-deficient strain did not grow in medium supplemented
with either quinate or shikimate as sole carbon sources. There was no discernible
difference in growth rate between wild-type and a cgR_1216-deficient strain.
Enzymatic assays showed that AroE both reduced 3-dehydroshikimate, using
NADPH as cofactor, and oxidized shikimate, the reverse reaction, using
NADP(+) as cofactor. The reduction reaction was ten times faster than the
oxidation. QsuD reduced 3-dehydroquinate using NADH and oxidized quinate
using NAD(+) as cofactor. Different from the other two homologues, the
product of cgR_1216 displayed considerably lower enzyme activity for both
the reduction and the oxidation. The catalytic reaction of QsuD and AroE
was highly susceptible to pH. Furthermore, reduction of 3-dehydroshikimate
by AroE was inhibited by high concentrations of shikimate, but neither
quinate nor aromatic amino acids had any effect on the reaction. Expression
of qsuD mRNA was strongly enhanced in the presence of shikimate, whereas
that of cgR_1216 and aroE decreased. We conclude that while AroE is the
main catalyst for shikimate production in the shikimate pathway, QsuD is
essential for quinate/shikimate utilization.