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The shikimate pathway is the biosynthetic pathway by which the aromatic amino acids [C Abell book chapter in "Comprehensive Natural Products Chemistry - Vol. 1", ed. U Sankawa, 1999, Elsevier, Amsterdam, pp 573-607, ISBN: 0080431534 (v.1)], phenylalanine, tyrosine and tryptophan are assembled. The pathway is present in plants, microorganisms and fungi but not mammals. It is the target for Glyphosate, a very important herbicide.

Our interests were to understand the enzymology of the pathway and we used detailed knowledge of the mechanism and structure of specific enzymes to design novel enzyme inhibitors. Such compounds could potentially be herbicides, fungicides, antibiotics or antiparasitic agents.

Our studies were focused on two areas:

The mechanism and structure of chorismate-utilising enzymes

Formation of p-aminobenzoate

We have previously shown that (6R)- and (6S)-6-fluoroEPSPs are potent inhibitors of chorismate synthase. Incubation of (6R)-6-fluoroEPSP with chorismate synthase provided the first evidence for the novel radical mechanism used by this enzyme while (6S)-6-fluoroEPSP is slowly converted into 2-fluorochorismate. We subsequently showed that 2-fluorochorismate irreversibly inhibited PabB by modifying the active site residue Lys274. This was a key piece of evidence in the discovery of the mechanism of this enzyme. We were the first group to detect an unprecedented covalent intermediate.

Formation of salicylate

We have characterised the first salicylate synthase, Irp9 from Yersinia. We solved the X-ray crystal structure with and without the product bound and studied the relationship to the structurally homologous enzyme TrpE. Based on their close structural similarity we have used site directed mutagenesis to convert Irp9 into an anthranilate synthase. 

Active site of Irp9 with salicyclate and pyruvate bound:

Developing inhibitors of type II dehydroquinase

Dehydroquinase catalyses the dehydration of dehydroquinate to form dehydroshikimate. The type I enzyme involves an imine intermediate and catalyses a syn elimination with loss of the equatorial C-2 hydrogen. The mechanism of the type II enzyme proceeds through an enolate and involves loss of the axial hydrogen at C-2 in an anti elimination. On the basis of these mechanistic differences we designed first generation inhibitors that are specific to type I and type II enzymes. Insights into the structure of type II dehydroquinase have led to a new strategy for developing potent inhibitors of the enzyme.

Related Publications 

S BALASUBRAMANIAN, C ABELL – Tetrahedron Letters (1991) 32, 963
Observation of an isotope effect in the chorismate synthase reaction
S BALASUBRAMANIAN, C ABELL, JR COGGINS – Journal of the American Chemical Society (2002) 112, 8581
Observation of a Secondary Tritium Isotope Effect in the Chorismate Synthase Reaction
S Balasubramanian, JR Coggins, C Abell – Biochemistry (2002) 34, 341
Escherichia coli chorismate synthase: a deuterium kinetic-isotope effect under single-turnover and steady-state conditions shows that a flavin intermediate forms before the C-(6proR)-H bond is cleaved.
S Bornemann, S Balasubramanian, JR Coggins, C Abell, DJ Lowe, RN Thorneley – The Biochemical journal (1995) 305 ( Pt 3), 707
Comparison of the substrate specificity of type I and type II dehydroquinases with 5-deoxy- and 4,5-dideoxy-dehydroquinic acid
JM Harris, WJ Watkins, AR Hawkins, JR Coggins, C Abell – Journal of the Chemical Society Perkin Transactions 1 (1996)2371
MN RAMJEE, S BALASUBRAMANIAN, C ABELL, JR COGGINS, GM DAVIES, TR HAWKES, DJ LOWE, RNF THORNELEY – Journal of the American Chemical Society (2002) 114, 3151
Enzymatic synthesis of (6R)- and (6S)-fluoroshikimic acids
PJ DUGGAN, E PARKER, J COGGINS, C ABELL – Bioorganic & Medicinal Chemistry Letters (1995) 5, 2347
Synthesis of (2R)-2-bromodehydroquinic acid and (2R)-2-fluorodehydroquinic acid
MK Manthey, C GonzalezBello, C Abell – Journal of the Chemical Society, Perkin Transactions 1 (1997)625
Derailing Dehydroquinate Synthase by Introducing a Stabilizing Stereoelectronic Effect in a Reaction Intermediate
EJ Parker, JR Coggins, C Abell – J Org Chem (1997) 62, 8582
Synthesis of 2-Bromo- and 2-Fluoro-3-dehydroshikimic Acids and 2-Bromo- and 2-Fluoroshikimic Acids Using Synthetic and Enzymatic Approaches
C Gonzalez-Bello, MK Manthey, JH Harris, AR Hawkins, JR Coggins, C Abell – The Journal of Organic Chemistry (1998) 63, 1591
Mechanistic studies on type I and type II dehydroquinase with (6R)- and (6S)-6-fluoro-3-dehydroquinic acids.
EJ Parker, C González Bello, JR Coggins, AR Hawkins, C Abell – Bioorganic & medicinal chemistry letters (2000) 10, 231
Irreversible inhibition of type I dehydroquinase by substrates for type II dehydroquinase.
CG Bello, JM Harris, MK Manthey, JR Coggins, C Abell – Bioorganic & Medicinal Chemistry Letters (2000) 10, 407
Inhibition of chorismate synthase by (6R)- and (6S)-6-fluoro-5-enolpyruvylshikimate 3-phosphate
S BALASUBRAMANIAN, GM DAVIES, JR COGGINS, C ABELL – Journal of the American Chemical Society (2002) 113, 8945
Escherichia coli chorismate synthase catalyzes the conversion of (6S)-6-fluoro-5-enolpyruvylshikimate-3-phosphate to 6-fluorochorismate: Implications for the enzyme mechanism and the antimicrobial action of (6S)-6-fluoroshikimate
S Bornemann, MK Ramjee, S Balasubramanian, C Abell, JR Coggins, DJ Lowe, RN Thorneley – Journal of Biological Chemistry (1995) 270, 22811
Identification of 4-amino-4-deoxychorismate synthase as the molecular target for the antimicrobial action of (6S)-6-fluoroshikimate
EMM Bulloch, MA Jones, EJ Parker, AP Osborne, E Stephens, GM Davies, JR Coggins, C Abell – J Am Chem Soc (2004) 126, 9912
Detection of Covalent Intermediates Formed in the Reaction of 4-Amino-4-deoxychorismate Synthase
EMM Bulloch, C Abell – ChemBioChem (2005) 6, 832
Salicylate biosynthesis: Overexpression, purification, and characterization of Irp9, a bifunctional salicylate synthase from Yersinia enterocolitica
O Kerbarh, A Ciulli, NI Howard, C Abell – Journal of Bacteriology (2005) 187, 5061
Crystal structures of Yersinia enterocolitica salicylate synthase and its complex with the reaction products salicylate and pyruvate.
O Kerbarh, DY Chirgadze, TL Blundell, C Abell – Journal of molecular biology (2006) 357, 524
Nucleophile Selectivity of Chorismate‐Utilizing Enzymes
O Kerbarh, A Ciulli, DY Chirgadze, TL Blundell, C Abell – ChemBioChem (2007) 8, 622
Observation of an imine intermediate on dehydroquinase by electrospray mass spectrometry
A SHNEIER, C KLEANTHOUS, R DEKA, JR COGGINS, C ABELL – Journal of the American Chemical Society (2002) 113, 9416
Enzymes that exploit imines - one way or the other
C Abell – Biochem Soc Trans (1998) 26, 310
Evidence from kinetic isotope studies for an enolate intermediate in the mechanism of type II dehydroquinases
JM Harris, C Gonzalez-Bello, C Kleanthous, AR Hawkins, JR Coggins, C Abell – Biochemical Journal (1996) 319, 333
Evidence for opposite stereochemical courses for the reaction catalysed by type I and type II dehydrocquinases
A SHNEIER, J HARRIS, C KLEANTHOUS, JR COGGINS, AR HAWKINS, C ABELL – Bioorganic & Medicinal Chemistry Letters (1993) 3, 1399
Different mechanistic and stereochemical courses for the reactions catalysed by type I and type II dehydroquinases
J HARRIS, C KLEANTHOUS, JR COGGINS, AR HAWKINS, C ABELL – Journal of the Chemical Society, Chemical Communications (1993)1080
Selective Inhibition of Type II Dehydroquinases
M Frederickson, EJ Parker, AR Hawkins, JR Coggins, C Abell – The Journal of Organic Chemistry (1999) 64, 2612
Vinyl fluoride as an isoelectronic replacement for an enolate anion: Inhibition of type II dehydroquinases
M Frederickson, JR Coggins, C Abell – Chem Commun (Camb) (2002)1886
The Structure and Mechanism of the Type II Dehydroquinase from Streptomyces coelicolor.
AW Roszak, DA Robinson, T Krell, IS Hunter, M Fredrickson, C Abell, JR Coggins, AJ Lapthorn – Structure (2002) 10, 493
Design, synthesis and evaluation of bifunctional inhibitors of type II dehydroquinase.
MD Toscano, M Frederickson, DP Evans, JR Coggins, C Abell, C González-Bello – Org Biomol Chem (2003) 1, 2075
Rational design of new bifunctional inhibitors of type II dehydroquinase.
MD Toscano, KA Stewart, JR Coggins, AJ Lapthorn, C Abell – Organic & biomolecular chemistry (2005) 3, 3102
pH-tuneable binding of 2′-phospho-ADP-ribose to ketopantoate reductase: a structural and calorimetric study
A Ciulli, CMC Lobley, KL Tuck, AG Smith, TL Blundell, C Abell – Acta crystallographica. Section D, Biological crystallography (2007) 63, 171