PDBsum entry: 2f1f

Transferase

PDB id: 2f1f

Contents

Protein chains

163 a.a. *

Ligands

1PE

P33

Metals

_MG ×6

Waters ×258

* Residue conservation analysis

PDB id:

2f1f

Name:

Transferase

Title:

Crystal structure of the regulatory subunit of acetohydroxyacid synthase isozyme iii from e. Coli

Structure:

Acetolactate synthase isozyme iii small subunit. Chain: a, b. Synonym: ahas-iii, acetohydroxy-acid synthase iii small subunit, als-iii. Engineered: yes

Source:

Escherichia coli. Organism_taxid: 562. Gene: ilvh, brnp. Expressed in: escherichia coli. Expression_system_taxid: 562.

Biol. unit:

Dimer (from PQS)

Resolution:

1.75Å R-factor: 0.174 R-free: 0.227

Authors:

A.Kaplun,M.Vyazmensky,Z.Barak,D.M.Chipman,B.Shaanan

Key ref:

A.Kaplun et al. (2006). Structure of the regulatory subunit of acetohydroxyacid synthase isozyme III from Escherichia coli. J Mol Biol, 357, 951-963. PubMed id: 16458324 DOI: 10.1016/j.jmb.2005.12.077

Date:

14-Nov-05 Release date: 24-Jan-06

Protein chains

P00894  (ILVH_ECOLI) -  Acetolactate synthase isozyme 3 small subunit

Seq: 163 a.a.

Struc: 163 a.a.*

* PDB and UniProt seqs differ at 1 residue position (black cross)

Enzyme reactions

• Enzyme class: E.C.2.2.1.6 - Acetolactate synthase.
• Pathway: Isoleucine and Valine Biosynthesis
• Reaction: 2 pyruvate = 2-acetolactate + CO₂
• Cofactor: Thiamine diphosphate

Molecule diagrams generated from .mol files obtained from the KEGG ftp site

 Gene Ontology (GO) functional annotation 

• Biological process: metabolic process (5 terms)
• Biochemical function: transferase activity (3 terms)

reference

DOI no: 10.1016/j.jmb.2005.12.077

J Mol Biol 357:951-963 (2006)

PubMed id: 16458324

Structure of the regulatory subunit of acetohydroxyacid synthase isozyme III from Escherichia coli.

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

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.

Selected figure(s)

Figure 2.
Figure 2. Overall view of AHAS III SSU. (a) View perpendicular to the dimer 2-fold axis. Chains A and B are coloured red and green, respectively. Secondary structure elements in the C-terminal domain of chain B are marked. The ACT domain composed of the N-terminal domains of both chains is at the top. The back-to-back disposition of the C-terminal domains is clearly seen at the bottom. (b) View after 90° rotation of the view in (a) around the dimer 2-fold. (c) View from the N-terminal ACT domain down the dimer 2-fold axis. Secondary structure elements in both N-terminal domains are marked. (d) View from the C-terminal domains down the dimer 2-fold axis emphasizing the back-to-back packing of the C-terminal β-sheets.

Figure 8.
Figure 8. Proposed location of valine binding site. (a) Schematic diagram of suggested effector site with bound valine. The diagram is based on the structure of AHAS III SSU, with valine located in the site as discussed in the text. The residues are all from a single polypeptide, except those with primed (′) numbers, which are part of the other subunit in a dimer. The shadowed area represents interactions among groups in a non-polar core, including the side-chain of the effector ligand, while polar interactions are represented by broken lines. (b) Superposition of the ACT-domains of AHAS III SSU (blue) and 3PGDH^10 (magenta) shown as C^α trace. Valine and serine are shown (CPK, labeled) in the proposed binding site of AHAS III SSU and the observed effector-binding site of 3PGDH, respectively. For clarity, only one ligand is shown in each case.

The above figures are reprinted by permission from Elsevier: J Mol Biol (2006, 357, 951-963) copyright 2006.

Figures were selected by the author.