Shikimate pathway by kk sahu sir

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. SHIKIMATE PATHWAY ENZYME INVOLVE IN SIKIMATE PATHWAY:- 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. SHIKIMATE PATHWAY 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. SHIKIMATE PATHWAY 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. SHIKIMATE PATHWAY

7. SHIKIMATE PATHWAY 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. SHIKIMATE PATHWAY 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. SHIKIMATE PATHWAY 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. SHIKIMATE PATHWAY 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 .