The shikimate pathway was discovered as the biosynthetic route to the aromatic amino acids phenylalanine, tyrosine, and tryptophan. This pathway has been found only in microorganisms and plants. Phenylalanine and tryptophan are essential components of animal diets, and animals synthesize tyrosine in a single step from phenylalanine.

1. Plant Secondary Metabolites
SHIKIMATE PATHWAY
By
KAUSHAL KUMAR SAHU
Assistant Professor (Ad Hoc)
Department of Biotechnology
Govt. Digvijay Autonomous P. G. College
Raj-Nandgaon ( C. G. )

2. INTRODUTION
• The shikimate pathway was discovered as the
biosynthetic route to the aromatic amino acids
phenylalanine, tyrosine, and tryptophan.
• This pathway has been found only in
microorganisms and plants. Phenylalanine and
tryptophan are essential components of animal
diets, and animals synthesize tyrosine in a
single step from phenylalanine.

3. SHIKIMATEPATHWAY
•DAHP Synthase
The first committed step in the biosynthesis of the three
aromatic amino acids is catalyzed by DAHP synthase. The
plant DAHP synthases are enzymes activated by Mn*+ and
tryptophan. Two families of genes encoding Mnz+-stimulated
DAHP synthases, the shkA and shkB types.
•3-Dehydroquinate Synthase
The second enzyme of the shikimate pathway, 3-
dehydroquinate synthase, requires catalytic amounts of NAD+
and a divalent cation for activity. The enzyme catalyzes a
seemingly very complex reaction involving an intramolecular
oxidation reduction at C5 of DAHP with very tight binding of
the NAD+ cofactor, the syn elimination of phosphate, and an
alicyclic ring formation.

4. SHIKIMATEPATHWAY 3-Dehydroquinate Dehydratase
3-dehydroquinate synthase is a monomeric enzyme 3-
dehydroquinate synthase is activated by inorganic phosphate,
and requires NAD+ for activity, although the reaction in total
is neutral when catalyzed by an enzyme. Dehydroquinate
synthase requires NAD+ and a cobalt cofactorR to catalyze
the conversion of 3-deoxy-D-arabino-heptulosonate 7-
phosphate into 3-dehydroquinate.
•Shikimate Kinase
In the fifth step of the pathway, a kinase phosphorylates shikimate to yield
shikimate 3-phosphate. Elimination of this phosphate two steps later leads
to the second double bond of the benzene ring. Sikimate has two type of
enzyme:- enzyme-1 and enzyme-2 Enzyme II may be the major activity
for chorismate biosynthesis.
Shikimate Dehydrogenase catalyzes the reversible NADPH-dependent
reaction of 3-dehydroshikimate to skikimate. The enzyme converts an
oxygen double bond to an OH- group to produce shikimate. The reaction
is NADPH dependent and reduces NADP.

5. SHIKIMATEPATHWAY EPSP Synthase
EPSP synthase is an essential element in the shikimate
pathway, transferring the enolypyruvyl group of
phosphoenolpyruvate (PEP) to shikimate-3-phosphate (S3P)
to form 5-enolpyruvyl-3-shikimate phosphate (EPSP) and
inorganic phosphate (Pi).
•Chorismate Synthase
The seventh and last step of the shikimate pathway is the
concerted lP-trans elimination of phosphate from EPSP to
yield Chorismate synthase, which catalyzes this reaction,
requires a reduced flavin nucleotide (FMNHz) as a
cofactor, even though the overall reaction is neutral.
Chorismate is converted by five distinct enzymes to
prephenate, anthranilate, aminodeoxychorismate,
isochorismate, and p-hydroxybenzoate, respectively. These
metabolites comprise the first committed intermediates in
the biosynthesis of Phe, Tyr, Trp.

6. SHIKIMATEPATHWAY

7. SHIKIMATEPATHWAY Function of amino acid synthesized by sikimate pathway:-
Tryptophane:-
Serotonin (a neurotransmitter), synthesized via
tryptophan hydroxylase. Serotonin, in turn, can be
converted to melatonin (a neurohormone), via N-
acetyltransferase and 5-hydroxyindole-O-
methyltransferase activities.
Auxin (a phytohormone) when sieve tube elements
undergo apoptosis tryptophan is converted to
auxins.
Tryptophan is a routine constituent of most protein-
based foods or dietary proteins. It is particularly
plentiful in chocolate, oats, dried dates, milk,
yogurt, cottage cheese, red meat, eggs, fish,
poultry, sesame, chickpeas, sunflower seeds,
pumpkin seeds, corn, spirulina, bananas, and
peanuts.

8. SHIKIMATEPATHWAY
TYROSINE
A tyrosine residue also plays an important role in
photosynthesis. In chloroplasts (photosystem II),
it acts as an electron donor in the reduction of
oxidized chlorophyll. In this process, it
undergoes deprotonation of its phenolic OH-
group. This radical is subsequently reduced in the
photosystem II by the four core manganese
clusters.
Tyrosine, which can also be synthesized in the
body from phenylalanine, is found in many high-
protein food products such as chicken, turkey,
fish, peanuts, almonds, avocados, milk, cheese,
yogurt, cottage cheese, lima beans, pumpkin
seeds, sesame seeds, bananas, and soy products.

9. SHIKIMATEPATHWAY
PHENYLALANINE
Phenylalanine is a precursor for tyrosine, the
monoamine signaling molecules dopamine,
norepinephrine (noradrenaline), and
epinephrine (adrenaline), and the skin pigment
melanin.
Phenylalanine is the starting compound used
in the flavonoid biosynthesis. Lignan is
derived from phenylalanine and from tyrosine.
Phenylalanine is converted to cinnamic acid
by the enzyme phenylalanine ammonia-lyase.

10. SHIKIMATEPATHWAY
Importance
Use of mutant EPSPS genes:-
An EPSPS mutant gene that conferred resistance to
glyphosate was first detected in the bacterium
Salmonella typhimurium . it was found that a single
base substitution (C to T) resulted in the change of an
amino acid from proline to serine in EPSPS. This
modified enzyme cannot bind to glyphosate , and thus
provide resistance.
Over expression of crop plant EPSPS gene:-
An overexpressing gene of EPSPS was detected in
Pentunia . this expression was found to be due to gene
amplification rather than an increased expression of
the gene. The increased expression EPSPS in
transgenic plant provide resistance to glyphosate.