Biological Assembly 1  

 3D View: Structure | 1D-3D View | Electron Density | Validation Report | Ligand Interaction

Global Symmetry: Dihedral - D2  (3D View)
Global Stoichiometry: Homo 4-mer - A4 

Biological assembly 1 assigned by authors and generated by PISA (software)

Macromolecule Content

• Total Structure Weight: 114.86 kDa 
• Atom Count: 8212 
• Modelled Residue Count: 1028 
• Deposited Residue Count: 1044 
• Unique protein chains: 1

1QG6

CRYSTAL STRUCTURE OF E. COLI ENOYL ACYL CARRIER PROTEIN REDUCTASE IN COMPLEX WITH NAD AND TRICLOSAN

• PDB DOI: 10.2210/pdb1QG6/pdb

• Classification: OXIDOREDUCTASE
• Organism(s): Escherichia coli
• Expression System: Escherichia coli BL21
• Mutation(s): No 


• Deposited: 1999-04-20 Released: 1999-09-21 
• Deposition Author(s): Rowsell, S., Pauptit, R.A.

---

Experimental Data Snapshot

• Method: X-RAY DIFFRACTION
• Resolution: 1.90 Å
• R-Value Free: 0.207 
• R-Value Work: 0.202 

Literature

Kinetic and structural characteristics of the inhibition of enoyl (acyl carrier protein) reductase by triclosan.

Ward, W.H., Holdgate, G.A., Rowsell, S., McLean, E.G., Pauptit, R.A., Clayton, E., Nichols, W.W., Colls, J.G., Minshull, C.A., Jude, D.A., Mistry, A., Timms, D., Camble, R., Hales, N.J., Britton, C.J., Taylor, I.W.

(1999) Biochemistry 38: 12514-12525

• PubMed: 10493822 
• DOI: 10.1021/bi9907779
• Primary Citation of Related Structures:  
  1QG6


• PubMed Abstract: 
  

Triclosan is used widely as an antibacterial agent in dermatological products, mouthwashes, and toothpastes. Recent studies imply that antibacterial activity results from binding to enoyl (acyl carrier protein) reductase (EACPR, EC 1.3.1.9). We first recognized the ability of triclosan to inhibit EACPR from Escherichia coli in a high throughput screen where the enzyme and test compound were preincubated with NAD(+), which is a product of the reaction. The concentration of triclosan required for 50% inhibition approximates to 50% of the enzyme concentration, indicating that the free compound is depleted by binding to EACPR. With no preincubation or added NAD(+), the degree of inhibition by 150 nM triclosan increases gradually over several minutes. The onset of inhibition is more rapid when NAD(+) is added. Gel filtration and mass spectrometry show that inhibition by triclosan is reversible. Steady-state assays were designed to avoid depletion of free inhibitor and changes in the degree of inhibition. The results suggest that triclosan binds to E-NAD(+) complex, with a dissociation constant around 20-40 pM. Triclosan follows competitive kinetics with respect to NADH, giving an inhibition constant of 38 pM at zero NADH and saturating NAD(+). Uncompetitive kinetics are observed when NAD(+) is varied, giving an inhibition constant of 22 pM at saturating NAD(+). By following regain of catalytic activity after dilution of EACPR that had been preincubated with triclosan and NAD(+), the rate constant for dissociation of the inhibitor (k(off)) is measured as 1.9 x 10(-4) s(-1). The association rate constant (k(on)) is estimated as 2.6 x 10(7) s(-1) M(-1) by monitoring the onset of inhibition during assays started by addition of EACPR. As expected, the ratio k(off)/k(on) = 7.1 pM is similar to the inhibition constants from the steady-state studies. The crystal structure of E. coli EACPR in a complex with coenzyme and triclosan has been determined at 1.9 A resolution, showing that this compound binds in a similar site to the diazaborine inhibitors. The high affinity of triclosan appears to be due to structural similarity to a tightly bound intermediate in catalysis.

---

Organizational Affiliation: 

AstraZeneca, Mereside, Macclesfield, Cheshire, U.K. [e-mail]

Macromolecules

Entity ID: 1
Molecule	Chains	Sequence Length	Organism	Details	Image
PROTEIN (ENOYL-[ACYL-CARRIER PROTEIN] REDUCTASE)	A, B, C, D	261	Escherichia coli	Mutation(s): 0  Gene Names: fabI EC: 1.3.1.9
UniProt
Find proteins for P0AEK4 (Escherichia coli (strain K12)) Explore P0AEK4  Go to UniProtKB:  P0AEK4

Small Molecules

Ligands 2 Unique
ID	Chains	Name / Formula / InChI Key	2D Diagram
NAD	E [auth A], G [auth B], I [auth C], K [auth D]	NICOTINAMIDE-ADENINE-DINUCLEOTIDE C21 H27 N7 O14 P2 BAWFJGJZGIEFAR-NNYOXOHSSA-N
TCL	F [auth A], H [auth B], J [auth C], L [auth D]	TRICLOSAN C12 H7 Cl3 O2 XEFQLINVKFYRCS-UHFFFAOYSA-N

Binding Affinity Annotations
ID	Source	Binding Affinity
TCL	Binding MOAD:  1QG6	Kd: 0.02 (nM) from 1 assay(s)
	BindingDB:  1QG6	IC50: min: 5, max: 900 (nM) from 3 assay(s)

Experimental Data & Validation

Experimental Data

• Method: X-RAY DIFFRACTION
• Resolution: 1.90 Å
• R-Value Free: 0.207 
• R-Value Work: 0.202 
• Space Group: P 1 2₁ 1

Unit Cell:

Length ( Å )	Angle ( ˚ )
a = 74.16	α = 90
b = 80.29	β = 104.46
c = 82.75	γ = 90

Software Package:

Software Name	Purpose
AMoRE	phasing
X-PLOR	refinement
MOSFLM	data reduction
CCP4	data scaling

Structure Validation

Entry History 

Deposition Data

• Deposited Date: 1999-04-20 
• Released Date: 1999-09-21 
Deposition Author(s): Rowsell, S., Pauptit, R.A.

Revision History  

• Version 1.0: 1999-09-21
  Type: Initial release
  
• Version 1.1: 2008-04-26
  Changes: Version format compliance
• Version 1.2: 2011-07-13
  Changes: Version format compliance