Функция белка PdxJ
Работа с программой Internet Explorer
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=21340789&dopt=Abstract
Structural basis for the function of pyridoxine 5'-phosphate synthase.
Franco MG, Laber B, Huber R, Clausen T.
Max-Planck-Institut fur Biochemie, Abteilung Strukturforschung, D-82152 Planegg-Martinsried, Germany.
BACKGROUND:
Pyridoxal 5'-phosphate is the active form of vitamin B(6) that acts as
an essential, ubiquitous coenzyme in amino acid metabolism. In
Escherichia coli, the pathway of the de novo biosynthesis of vitamin
B(6) results in the formation of pyridoxine 5'-phosphate (PNP), which
can be regarded as the first synthesized B(6) vitamer. PNP synthase
(commonly referred to as PdxJ) is a homooctameric enzyme that catalyzes
the final step in this pathway, a complex intramolecular condensation
reaction between 1-deoxy-D-xylulose-5'-phosphate and
1-amino-acetone-3-phosphate. RESULTS: The crystal structure of E. coli
PNP synthase was solved by single isomorphous replacement with
anomalous scattering and refined at a resolution of 2.0 A. The monomer
of PNP synthase consists of one compact domain that adopts the abundant
TIM barrel fold. Intersubunit contacts are mediated by three additional
helices, respective to the classical TIM barrel helices, generating a
tetramer of symmetric dimers with 422 symmetry. In the shared active
sites of the active dimers, Arg20 is directly involved in substrate
binding of the partner monomer. Furthermore, the structure of PNP
synthase with its physiological products, PNP and P(i), was determined
at 2.3 A resolution, which provides insight into the dynamic action of
the enzyme and allows us to identify amino acids critical for enzymatic
function. CONCLUSION: The high-resolution structures of the free enzyme
and the enzyme-product complex of E. coli PNP synthase suggest
essentials of the enzymatic mechanism. The main catalytic features are
active site closure upon substrate binding by rearrangement of one
C-terminal loop of the TIM barrel, charge-charge stabilization of the
protonated Schiff-base intermediate, the presence of two phosphate
binding sites, and a water channel that penetrates the beta barrel and
allows the release of water molecules in the closed state. All related
PNP synthases are predicted to fold into a similar TIM barrel pattern
and have comparable active site architecture. Thus, a common mechanism
can be anticipated.
Главная страница