Overview for MACiE Entry M0283
EC Number: 18.104.22.168 (A member of the Transferases, Transferring nitrogenous groups, Transaminases)
Enzyme Name: aminodeoxychorismate synthase
Biological Species: Escherichia coli (Bacteria)
Catalytic Chain UniprotKB Accession Codes:
- P05041 - Para-aminobenzoate synthase component 1
Representative PDB Code: 1k0g - THE CRYSTAL STRUCTURE OF AMINODEOXYCHORISMATE SYNTHASE FROMPHOSPHATE GROWN CRYSTALS (Resolution = 2.05 Å).
Catalytic CATH Codes:
"Other" CATH Codes:
Display structure information
Overall Comment: The enzyme is composed of two parts, PabA and PabB. In the absence of PabA and glutamine, PabB will still convert ammonia and chorismate into 4-amino-4-deoxychorismate. PabA, a 21kDa subunit, converts glutamine into glutamate only in the presence of stoichiometric amounts of PabB and provides the nucleophile (ammonia) via hydrolysis of glutamine to the PabA subunit. The crystal structure used here is only of PabB, there doesn't appear to be a structure available of both components together. Of the two domains present, the Chlorismate Superfamily Fold is thought to be the site of catalysis, but the second domain, situated in the N-terminus is thought to be involved in regulating an inhibitory feedback mechanism involving tryptophan.
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Stepwise Description of the Reaction
|Step 1||Chorismate is attacked at C(2) by the nucleophilic Lys274, resulting in the conjugate elimination of water from C(4). Glu258 acts as a general acid to the departing water.|
|Step 2||The imidazol of His168 is proposed to act as a general base towards Cys79, activating the thiol towards nucleophilic attack at the glutamine carbonyl.|
|Step 3||The anionic tetrahedral intermediate collapses. This generates the ammonia which is subsequently transferred to the aminodeoxychorismate synthase catalytic centre in the PapB subunit through a specific channel.|
|Step 4||Ammonia formed from the hydrolysis of glutamine attacks at the C(4) position of the chorismate-enzyme adduct, eliminating Lys274.|
|Step 5||Glu258 acts as a general base, abstracting a proton from the C(4) amino group and regenerating the synthase catalytic site.|
|Step 6||His168 deprotonates the water, which attacks the enzyme-glutamine complex, forming a tetrahedral intermediate.|
|Step 7||The tetrahedral intermediate collapses, eliminating Cys79, which deprotonates His168.|
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Catalytic Residues Involved
||Location of Function
- J. F. Parsons et al. (2002), Biochemistry, 41, 2198-2208. Structure of Escherichia coli aminodeoxychorismate synthase: architectural conservation and diversity in chorismate-utilizing enzymes.
- K. T. Ziebart et al. (2010), Biochemistry, 49, 2851-2859. Nucleophile specificity in anthranilate synthase, aminodeoxychorismate synthase, isochorismate synthase, and salicylate synthase.
- Z. He et al. (2004), J. Am. Chem. Soc., 126, 2378-2385. Conservation of mechanism in three chorismate-utilizing enzymes.
- Z. He et al. (2006), Biochemistry, 45, 5019-5028. Direct detection and kinetic analysis of covalent intermediate formation in the 4-amino-4-deoxychorismate synthase catalyzed reaction.
- F. Massiere et al. (1998), Cell. Mol. Life Sci., 54, 205-222. The mechanism of glutamine-dependent amidotransferases.
- B. Roux et al. (1993), Biochemistry, 32, 3763-3768. p-Aminobenzoate synthesis in Escherichia coli: mutational analysis of three conserved amino acid residues of the amidotransferase PabA.
Homologue information for M0283 (1k0g)
MACiE Homologues (within the PDB)
MACiE Homologues (within UniprotKB/SwissProt)
Entries with at least one Catalytic CATH code in common (different mechanisms):
|M0314 ||anthranilate synthase |
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