Aminodeoxychorismate synthase

4-amino-4-deoxychorismate synthase

Aminodeoxychorismate synthase
Identifiers
EC number 2.6.1.85
CAS number 132264-37-0
Databases
IntEnz IntEnz view
BRENDA BRENDA entry
ExPASy NiceZyme view
KEGG KEGG entry
MetaCyc metabolic pathway
PRIAM profile
PDB structures RCSB PDB PDBe PDBsum
Gene Ontology AmiGO / EGO

In enzymology, an aminodeoxychorismate synthase (EC 2.6.1.85) is an enzyme that catalyzes the chemical reaction

chorismate + L-glutamine \rightleftharpoons 4-amino-4-deoxychorismate + L-glutamate

Thus, the two substrates of this enzyme are chorismate and L-glutamine, whereas its two products are 4-amino-4-deoxychorismate and L-glutamate.[1][2][3][4]

It is part of a pathway for the biosynthesis of para-aminobenzoic acid (PABA); a precursor for the production of folates. Folates are family of cofactors that are essential for living organisms. Folate cofactors are used in several one-carbon transfer reactions required during the synthesis of essential metabolites, including methionine and thymidylate.[1]

Aminodeoxychorsimate synthase (PabB), a 51 kDa protein in E. coli, is encoded by the gene pabB.[2] 4-amino-4-deoxychorismate, the product of PabB, can be converted to para-aminobenzoic acid by the enzyme 4-amino-4-deoxychorismate lyase (PabC).

Nonmenclature

This enzyme belongs to the class of transferases. This means that aminodeoxychorismate synthase catalyzes the transfer of one functional group from a molecule to another. Specifically, aminodeoxychorismate synthase is a transaminase that transfers an amino group to a keto acid. The systematic name is Chorismate:L-glutamine aminotransferase. Formerly aminodeoxychorismate synthase was referred to as PABA synthase; however this name is no longer recommended[5] as it is understood that the formation of PABA requires the action of a further enzyme (4-amino-4-deoxychorismate lyase).

Common names that the enzyme goes by are:[6]

Reaction

In certain microbial species such as Escherichia coli, aminodeoxychorismate synthase is a heterodimeric complex composed of two proteins, glutamine amidotransferase (PabA) and 4-amino-4-deoxychorismate synthase (PabB). In other species such as plants or lower eukaryotes an enzyme comprising a single polypeptide performs both reactions.

In Escherichia coli, the reaction is a two step process. Glutamine amidotransferase (PabA) and 4-amino-4-deoxychorismate synthase (PabB) form a heterodimeric complex that catalyzes the synthesis of 4-amino-4-deoxychorismate. The first step occurs with PabA abstracting ammonia from glutamine. The second step occurs when PabB reacts both substrates (chorismate and ammonia) to synthesize 4-amino-4-deoxychorsimate.

In plants such as Arabidopsis thaliana, aminodeoxychorsimate synthase is a monomeric enzyme that carries out both steps of the reaction.[1]

Structure

Aminodeoxychorismate synthase (PabB) is either a heterodimeric or monomeric enzyme depending on what organism it is from. The enzyme has 452-residues and consists of both alpha and beta folds that is very similar to some types of anthranilate synthase. The core of PabB consists of two domains that form a beta sandwich. Also, it has helices and loops around the outside of its core.[3] The chorsimate binding site on PabB consists of amino acids residues that make up beta sheet core and the two key alpha helices.[4]

Certain aminodeoxychorismate synthase enzymes contain an additional binding site for tryptophan, thought to be a non-functional vestigial binding site. It is believed that aminodeoxychorismate synthase may have evolved from anthranilate synthase (TrpE) - an enzyme that catalyses the production of an intermediate on the path to tryptophan.[3]

Homologues

Enzymes with similar structures to aminodeoxychorismate synthase are:

A common feature among this list of enzymes is that they all utilize chorismate as a substrate.

Anti-folate drug target

Aminodeoxychorismate synthase is targeted by the antibiotics atrop-abyssomycin C and 6-fluoroshikimic acid. By inhibiting the production of an intermediate on the pathway to PABA, folate levels are depleted. Without sufficient folate, DNA and protein synthesis are severely impaired.

References

  1. 1 2 3 SAHR, Tobias (May 15, 2006). "Folate synthesis in plants: purification, kinetic properties, and inhibition of aminodeoxychorismate synthase". Biochem J. 396(Pt. 1):157-162 396 (1): 157–62. doi:10.1042/BJ20051851. PMC 1449997. PMID 16466344.
  2. 1 2 Ye, Qi-Zhuang (August 23, 1990). "p-Aminobenzoate synthesis in Escherichia coli: Purificiation and characterization of PabB as aminodeoxychorsimate synthase and enzyme X as aminodeoxychorsimate lyase". Proc Natl Acad Sci USA 87 (23): 9391–5. Bibcode:1990PNAS...87.9391Y. doi:10.1073/pnas.87.23.9391. PMC 55171. PMID 2251281.
  3. 1 2 3 Parsons, James (November 21, 2001). "Structure of Escherichia coli Aminodeoxychorismate Synthase: Architectural Conservation and Diversity in Chorismate-Utilizing Enzymes". Biochemistry 41 (7): 2198–2208. doi:10.1021/bi015791b. PMID 11841211.
  4. 1 2 Bera, Asim (December 21, 2013). "Structure of Aminodeoxychorismate Synthase from Stenotrophomonas maltophilia". Biochemistry 51 (51): 10208–17. doi:10.1021/bi301243v. PMC 3532939. PMID 23230967.
  5. ↑ Green JM, Nichols BP (1991). "p-Aminobenzoate biosynthesis in Escherichia coli. Purification of aminodeoxychorismate lyase and cloning of pabC". J. Biol. Chem. 266 (20): 12971–5. PMID 2071583.
  6. ↑ "ENZYME: 2.6.1.85". KEGG.
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