Crystal structure of the regulatory subunit of acetohydroxyacid synthase isozyme III from E. coli

Experimental Data Snapshot

  • Resolution: 1.75 Å
  • R-Value Free: 0.227 
  • R-Value Work: 0.171 
  • R-Value Observed: 0.174 

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Structure of the Regulatory Subunit of Acetohydroxyacid Synthase Isozyme III from Escherichia coli.

Kaplun, A.Vyazmensky, M.Zherdev, Y.Belenky, I.Slutzker, A.Mendel, S.Barak, Z.Chipman, D.M.Shaanan, B.

(2006) J Mol Biol 357: 951-963

  • DOI: https://doi.org/10.1016/j.jmb.2005.12.077
  • Primary Citation of Related Structures:  

  • PubMed Abstract: 

    The enzyme acetohydroxyacid synthase (AHAS) catalyses the first common step in the biosynthesis of the three branched-chain amino acids. Enzymes in the AHAS family generally consist of regulatory and catalytic subunits. Here, we describe the first crystal structure of an AHAS regulatory subunit, the ilvH polypeptide, determined at a resolution of 1.75 A. IlvH is the regulatory subunit of one of three AHAS isozymes expressed in Escherichia coli, AHAS III. The protein is a dimer, with two beta alpha beta beta alpha beta ferredoxin domains in each monomer. The two N-terminal domains assemble to form an ACT domain structure remarkably close to the one predicted by us on the basis of the regulatory domain of 3-phosphoglycerate dehydrogenase (3PGDH). The two C-terminal domains combine so that their beta-sheets are roughly positioned back-to-back and perpendicular to the extended beta-sheet of the N-terminal ACT domain. On the basis of the properties of mutants and a comparison with 3PGDH, the effector (valine) binding sites can be located tentatively in two symmetrically related positions in the interface between a pair of N-terminal domains. The properties of mutants of the ilvH polypeptide outside the putative effector-binding site provide further insight into the functioning of the holoenzyme. The results of this study open avenues for further studies aimed at understanding the mechanism of regulation of AHAS by small-molecule effectors.

  • Organizational Affiliation

    Department of Life Sciences, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
Acetolactate synthase isozyme III small subunit
A, B
164Escherichia coliMutation(s): 0 
Gene Names: ilvHbrnP
Find proteins for P00894 (Escherichia coli (strain K12))
Explore P00894 
Go to UniProtKB:  P00894
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupP00894
Sequence Annotations
  • Reference Sequence
Small Molecules
Ligands 3 Unique
IDChains Name / Formula / InChI Key2D Diagram3D Interactions
Query on P33

Download Ideal Coordinates CCD File 
J [auth B]3,6,9,12,15,18-HEXAOXAICOSANE-1,20-DIOL
C14 H30 O8
Query on 1PE

Download Ideal Coordinates CCD File 
C10 H22 O6
Query on MG

Download Ideal Coordinates CCD File 
C [auth A]
D [auth A]
F [auth B]
G [auth B]
H [auth B]
C [auth A],
D [auth A],
F [auth B],
G [auth B],
H [auth B],
I [auth B]
Experimental Data & Validation

Experimental Data

  • Resolution: 1.75 Å
  • R-Value Free: 0.227 
  • R-Value Work: 0.171 
  • R-Value Observed: 0.174 
  • Space Group: I 4
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 98.6α = 90
b = 98.6β = 90
c = 80γ = 90
Software Package:
Software NamePurpose
XSCALEdata scaling
PDB_EXTRACTdata extraction

Structure Validation

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Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2006-01-24
    Type: Initial release
  • Version 1.1: 2008-05-01
    Changes: Version format compliance
  • Version 1.2: 2011-07-13
    Changes: Version format compliance
  • Version 1.3: 2017-10-18
    Changes: Refinement description
  • Version 1.4: 2024-02-14
    Changes: Data collection, Database references, Derived calculations, Structure summary