{PDOC00635}
{PS00801; TRANSKETOLASE_1}
{PS00802; TRANSKETOLASE_2}
{BEGIN}
****************************
* Transketolase signatures *
****************************

Transketolase  (EC 2.2.1.1) (TK)   catalyzes  the   reversible  transfer  of a
two-carbon ketol unit from xylulose 5-phosphate to an aldose receptor, such as
ribose 5-phosphate, to  form  sedoheptulose  7-phosphate and glyceraldehyde 3-
phosphate. This enzyme, together with transaldolase, provides  a  link between
the glycolytic and pentose-phosphate pathways.

TK requires thiamine pyrophosphate as a cofactor. In most sources where TK has
been purified, it is a homodimer of approximately 70 Kd subunits. TK sequences
from a  variety  of  eukaryotic  and  prokaryotic  sources [1,2] show that the
enzyme has been evolutionarily conserved.

In the peroxisomes of    methylotrophic yeast Hansenula polymorpha, there is a
highly  related  enzyme, dihydroxy-acetone  synthase (DHAS) (EC 2.2.1.3) (also
known as   formaldehyde   transketolase),   which   exhibits  a  very  unusual
specificity by including formaldehyde amongst its substrates.

1-deoxyxylulose-5-phosphate synthase  (DXP  synthase)  [3] is an enzyme so far
found in  bacteria  (gene  dxs)  and  plants  (gene  CLA1) which catalyzes the
thiamine pyrophosphoate-dependent acyloin condensation reaction between carbon
atoms 2  and  3 of pyruvate and glyceraldehyde 3-phosphate to yield 1-deoxy-D-
xylulose-5-phosphate (dxp),   a  precursor  in  the  biosynthetic  pathway  to
isoprenoids, thiamine  (vitamin  B1), and pyridoxol (vitamin B6). DXP synthase
is evolutionary related to TK.

We selected two regions of TK as signature patterns. The first, located in the
N-terminal section, contains a histidine residue which appears to  function in
proton transfer  during  catalysis  [4].  The second, located in  the  central
section, contains conserved acidic residues  that are part of the active cleft
and may participate in substrate-binding [4].

-Consensus pattern: R-x(3)-[LIVMTA]-[DENQSTHKF]-x(5,6)-[GSN]-G-H-[PLIVMF]-
                    [GSTA]-x(2)-[LIMC]-[GS]
-Sequences known to belong to this class detected by the pattern: ALL,  except
 for Mycoplasma TK and human TK-2.
-Other sequence(s) detected in Swiss-Prot: 1.

-Consensus pattern: [GP]-[DEQGSANPHVT]-[DN]-G-[PAEQ]-[ST]-[HQ]-x-[PAGM]-
                    [LIVMYACNQS]-[DEFYWLA]-x(2)-[STAPG]-x(2)-[RGANQS]
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.

-Last update: December 2004 / Pattern and text revised.

[ 1] Abedinia M., Layfield R., Jones S.M., Nixon P.F., Mattick J.S.
     "Nucleotide and predicted amino acid sequence of a cDNA clone encoding
     part of human transketolase."
     Biochem. Biophys. Res. Commun. 183:1159-1166(1992).
     PubMed=1567394
[ 2] Fletcher T.S., Kwee I.L., Nakada T., Largman C., Martin B.M.
     "DNA sequence of the yeast transketolase gene."
     Biochemistry 31:1892-1896(1992).
     PubMed=1737042
[ 3] Sprenger G.A., Schorken U., Wiegert T., Grolle S., de Graaf A.A.,
     Taylor S.V., Begley T.P., Bringer-Meyer S., Sahm H.
     "Identification of a thiamin-dependent synthase in Escherichia coli
     required for the formation of the 1-deoxy-D-xylulose 5-phosphate
     precursor to isoprenoids, thiamin, and pyridoxol."
     Proc. Natl. Acad. Sci. U.S.A. 94:12857-12862(1997).
     PubMed=9371765
[ 4] Lindqvist Y., Schneider G., Ermler U., Sundstroem M.
     "Three-dimensional structure of transketolase, a thiamine diphosphate
     dependent enzyme, at 2.5 A resolution."
     EMBO J. 11:2373-2379(1992).
     PubMed=1628611

--------------------------------------------------------------------------------
PROSITE is copyrighted by the SIB Swiss Institute of Bioinformatics and
distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives
(CC BY-NC-ND 4.0) License, see https://prosite.expasy.org/prosite_license.html
--------------------------------------------------------------------------------

{END}