Результаты поиска в Интернете информации по функциям белка UbiC:
The crystal structure of chorismate lyase shows a new fold and a tightly retained product.
Gallagher DT, Mayhew M, Holden MJ, Howard A, Kim KJ, Vilker VL.
The enzyme chorismate lyase (CL) catalyzes the removal of pyruvate from chorismate to
produce 4-hydroxy benzoate (4HB) for the ubiquinone pathway. In Escherichia coli, CL
is monomeric, with 164 residues. We have determined the structure of the CL product
complex by crystallographic heavy-atom methods and report the structure at 1.4-A
resolution for a fully active double Cys-to-Ser mutant and at 2.0-A resolution for the
wild-type. The fold involves a 6-stranded antiparallel beta-sheet with no spanning
helices and novel connectivity. The product is bound internally, adjacent to the sheet,
with its polar groups coordinated by two main-chain amides and by the buried side-chain
s of Arg 76 and Glu 155. The 4HB is completely sequestered from solvent in a largely
hydrophobic environment behind two helix-turn-helix loops. The extensive product
binding that is observed is consistent with biochemical measurements of slow product
release and 10-fold stronger binding of product than substrate. Substrate binding
and kinetically rate-limiting product release apparently require the rearrangement
of these active-site-covering loops. Implications for the biological function of the
high product binding are considered in light of the unique cellular role of 4HB, which
is produced by cytoplasmic CL but is used by the membrane-bound enzyme 4HB
octaprenyltransferase.
Aerobic and anaerobic regulation of the ubiCA operon, encoding enzymes for the first
two committed steps of ubiquinone biosynthesis in Escherichia coli.
Soballe B, Poole RK.
The ubiCA operon of Escherichia coli encodes enzymes for the first two steps of ubiquinone
biosynthesis. A monolysogen (ubiC-lacZ operon fusion) was constructed to study ubiCA
regulation. Expression was higher during aerobic growth than anaerobically, and
increased with rate of oxygen supply. Although ubiquinone is implicated in antioxidant
roles, ubiC expression was not elevated in response to hydrogen peroxide or the redox
cycling agent, paraquat. Glucose repressed expression and mutation of cya (encoding
adenylate cyclase) increased expression. Anaerobically utilised electron acceptors
(nitrite, nitrate, fumarate) did not affect expression. ubiC expression appears to be
negatively regulated by Fnr and IHF.
Genetic engineering of plant secondary metabolism.
Accumulation of 4-hydroxybenzoate glucosides as a result of the expression of the bacterial
ubiC gene in tobacco.
Siebert M, Sommer S, Li SM, Wang ZX, Severin K, Heide L.
The ubiC gene of Escherichia coli encodes chorismate pyruvate lyase, an enzyme that
converts chorismate into 4-hydroxybenzoate (4HB) and is not normally present in plants
. The ubiC gene was expressed in Nicotiana tabacum L. plants under control of a
constitutive plant promoter. The gene product was targeted into the plastid by fusing
it to the sequence for the chloroplast transit peptide of the small subunit of
ribulose-1,5-bisphosphate carboxylase/oxygenase. Transgenic plants showed high
chorismate pyruvate-lyase activity and accumulated 4HB as beta-glucosides, with the
glucose attached to either the hydroxy or the carboxyl function of 4HB. The total
content of 4HB glucosides was approximately 0.52% of dry weight, which exceeded the
content of untransformed plants by at least a factor of 1000. Feeding experiments with
[1,7-13C2]shikimic acid unequivocally proved that the 4HB that was formed in the
transgenic plants was not derived from the conventional phenylpropanoid pathway but
from the newly introduced chorismate pyruvate-lyase reaction.