PDBsum entry 1qws

Oxidoreductase

PDB id: 1qws

Contents

Protein chains

727 a.a. *

Ligands

HEM ×4

Waters ×3033

* Residue conservation analysis

PDB id:

1qws

Name:

Oxidoreductase

Title:

Structure of the d181n variant of catalase hpii from e. Coli

Structure:

Catalase hpii. Chain: a, b, c, d. Synonym: hydroxyperoxidase ii. Engineered: yes. Mutation: yes

Source:

Escherichia coli. Organism_taxid: 562. Gene: kate. Expressed in: escherichia coli. Expression_system_taxid: 562.

Biol. unit:

Tetramer (from PQS)

Resolution:

1.90Å R-factor: 0.167 R-free: 0.220

Authors:

P.Chelikani,X.Carpena,I.Fita,P.C.Loewen

Key ref:

P.Chelikani et al. (2003). An electrical potential in the access channel of catalases enhances catalysis. J Biol Chem, 278, 31290-31296. PubMed id: 12777389 DOI: 10.1074/jbc.M304076200

Date:

03-Sep-03 Release date: 14-Oct-03

Protein chains

P21179  (CATE_ECOLI) -  Catalase HPII from Escherichia coli (strain K12)

Seq: 753 a.a.

Struc: 727 a.a.*

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

Enzyme reactions

• Enzyme class: E.C.1.11.1.6 - catalase.
• Reaction: 2 H2O2 = O2 + 2 H2O
• Cofactor: Heme; Mn(2+)

Heme (Bound ligand (Het Group name = HEM) matches with 95.45% similarity) Mn(2+)

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

reference

DOI no: 10.1074/jbc.M304076200

J Biol Chem 278:31290-31296 (2003)

PubMed id: 12777389

An electrical potential in the access channel of catalases enhances catalysis.

P.Chelikani, X.Carpena, I.Fita, P.C.Loewen.

ABSTRACT

Substrate H2O2 must gain access to the deeply buried active site of catalases through channels of 30-50 A in length. The most prominent or main channel approaches the active site perpendicular to the plane of the heme and contains a number of residues that are conserved in all catalases. Changes in Val169, 8 A from the heme in catalase HPII from Escherichia coli, introducing smaller, larger or polar side chains reduces the catalase activity. Changes in Asp181, 12 A from the heme, reduces activity by up to 90% if the negatively charged side chain is removed when Ala, Gln, Ser, Asn, or Ile are the substituted residues. Only the D181E variant retains wild type activity. Determination of the crystal structures of the Glu181, Ala181, Ser181, and Gln181 variants of HPII reveals lower water occupancy in the main channel of the less active variants, particularly at the position forming the sixth ligand to the heme iron and in the hydrophobic, constricted region adjacent to Val169. It is proposed that an electrical potential exists between the negatively charged aspartate (or glutamate) side chain at position 181 and the positively charged heme iron 12 A distant. The potential field acts upon the electrical dipoles of water generating a common orientation that favors hydrogen bond formation and promotes interaction with the heme iron. Substrate hydrogen peroxide would be affected similarly and would enter the active site oriented optimally for interaction with active site residues.

Selected figure(s)

Figure 3.
FIG. 3. a, schematic showing the distances among waters in the main channel of the D181E variant. The potential hydrogen bonds are shown as dashed lines, and the distances are expressed in Å. The water numbering is as in Fig. 2 and Table IV. b, stereo view oriented down the main channel toward the heme from Asp181. The slightly shifted location of the Glu side chain in the D181E variant is indicated in green. The water numbering is as in a.

Figure 4.
FIG. 4. Schematic of the main channel illustrating the presence of a negative charge (in green) on the side chain of Glu181 and a positive charge (in green) on the heme iron and the effect of the electrical potential between these two charges on the electrical dipoles of water in the channel and active site. The orientation of the electrical dipoles is indicated by the green arrow over each H[2]O. The location of the water molecules are those in subunit A of variant D181E.

The above figures are reprinted by permission from the ASBMB: J Biol Chem (2003, 278, 31290-31296) copyright 2003.

Figures were selected by an automated process.