Lactoperoxidase

 

Antimicrobial agent which utilizes hydrogen peroxide and thiocyanate (SCN) to generate the antimicrobial substance hypothiocyanous acid (HOSCN). Hypo(pseudo)halides, such as HOSCN, are powerful oxidants with antimicrobial activity, thus this reaction is thought to help protect the udder from infection and promote growth in newborn calves. Inhibits growth of the following bacterial species: E. coli, K. pneumoniae, P. aeruginosa, S. sonnei, S. saphrophyticus, S. epidermidis, and S. dysenteriae.

 

Reference Protein and Structure

Sequence
A5JUY8 UniProt (1.11.1.7) IPR029587 (Sequence Homologues) (PDB Homologues)
Biological species
Bubalus bubalis (Water buffalo) Uniprot
PDB
3fnl - Crystal Structure of the Complex of Buffalo Lactoperoxidase with Salicylhydroxamic Acid at 2.48 A Resolution (2.48 Å) PDBe PDBsum 3fnl
Catalytic CATH Domains
1.10.640.10 CATHdb (see all for 3fnl)
Cofactors
Heme b (1), Calcium(2+) (1)
Click To Show Structure

Enzyme Reaction (EC:1.11.1.7)

hydrogen peroxide
CHEBI:16240ChEBI
+
thiocyanate
CHEBI:18022ChEBI
+
hydron
CHEBI:15378ChEBI
→
hypothiocyanous acid
CHEBI:133907ChEBI
+
water
CHEBI:15377ChEBI
Alternative enzyme names: Japanese radish peroxidase, Extensin peroxidase, Guaiacol peroxidase, Heme peroxidase, Horseradish peroxidase (HRP), Lactoperoxidase, Oxyperoxidase, Protoheme peroxidase, Pyrocatechol peroxidase, Scopoletin peroxidase, Plant peroxidase, Soybean peroxidase (SBP), Coprinus cinereus peroxidase, Arthromyces ramosus peroxidase,

Enzyme Mechanism

Introduction

The thiocyanate ion, which is a physiological substrate for the mammalian enzyme, is placed almost parallel to the plane of the heme moiety with the sulfur atom being closer to the heme iron than its nitrogen atom. The first reaction in the mechanism of this enzyme is the formation of compound I utilising hydrogen peroxide, which acts as an electron acceptor. The native enzyme undergoes a two-electron oxidation. Two electrons are transferred from the enzyme to hydrogen peroxide which is reduced into water. Compound I is two oxidising equivalents above the native enzyme: one is in the oxyferryl heme center and the other is present as an organic cation located on the porphyrin ring.In the presence of a halogen (Cl-, Br-, or I-) or a pseudohalogen (SCN-), Compound I is reduced back to its native enzymatic form through a two-electron transfer while the (pseudo)halogen is oxidised into a hypo(pseudo)halide.

Catalytic Residues Roles

UniProt PDB* (3fnl)
Asp227, Thr301, Phe303, Asp305, Ser307 Asp110A, Thr184A, Phe186A, Asp188A, Ser190A Forms the calcium ion binding site. metal ligand
Asp225, Glu375 Asp108A, Glu258A These residues are covalently attached to the heme cofactor, helping to regulate its redox potential. covalently attached, alter redox potential
His468 His351A Acts as the distal ligand to the iron in heme. metal ligand
Gln222 Gln105A Helps to stabilise the reactive intermediates and transition states formed during the course of the reaction. transition state stabiliser
*PDB label guide - RESx(y)B(C) - RES: Residue Name; x: Residue ID in PDB file; y: Residue ID in PDB sequence if different from PDB file; B: PDB Chain; C: Biological Assembly Chain if different from PDB. If label is "Not Found" it means this residue is not found in the reference PDB.

Chemical Components

References

  1. Bafort F et al. (2014), Enzyme Res, 2014, 517164-. Mode of action of lactoperoxidase as related to its antimicrobial activity: a review. DOI:10.1155/2014/517164. PMID:25309750.
  2. Mak PJ et al. (2015), J Am Chem Soc, 137, 349-361. Resonance Raman spectroscopy reveals pH-dependent active site structural changes of lactoperoxidase compound 0 and its ferryl heme O-O bond cleavage products. DOI:10.1021/ja5107833. PMID:25506715.
  3. Sicking W et al. (2012), Chemistry, 18, 10937-10948. DFT calculations suggest a new type of self-protection and self-inhibition mechanism in the mammalian heme enzyme myeloperoxidase: nucleophilic addition of a functional water rather than one-electron reduction. DOI:10.1002/chem.201103477. PMID:22829409.
  4. Singh AK et al. (2012), Protein J, 31, 598-608. Bovine carbonyl lactoperoxidase structure at 2.0Å resolution and infrared spectra as a function of pH. DOI:10.1007/s10930-012-9436-3. PMID:22886082.
  5. Singh AK et al. (2011), Int J Biochem Mol Biol, 2, 328-339. Structural evidence for the order of preference of inorganic substrates in mammalian heme peroxidases: crystal structure of the complex of lactoperoxidase with four inorganic substrates, SCN, I, Br and Cl. PMID:22187667.
  6. Banerjee S et al. (2011), Biotechnol J, 6, 231-243. Bovine lactoperoxidase - a versatile one- and two-electron catalyst of high structural and thermal stability. DOI:10.1002/biot.201000375. PMID:21298808.
  7. Singh AK et al. (2010), J Biol Inorg Chem, 15, 1099-1107. First structural evidence for the mode of diffusion of aromatic ligands and ligand-induced closure of the hydrophobic channel in heme peroxidases. DOI:10.1007/s00775-010-0669-3. PMID:20461536.
  8. Sheikh IA et al. (2009), J Biol Chem, 284, 14849-14856. Structural evidence of substrate specificity in mammalian peroxidases: structure of the thiocyanate complex with lactoperoxidase and its interactions at 2.4 A resolution. DOI:10.1074/jbc.M807644200. PMID:19339248.
  9. Devarajan A et al. (2008), J Inorg Biochem, 102, 1549-1557. Effect of covalent links on the structure, spectra, and redox properties of myeloperoxidase--a density functional study. DOI:10.1016/j.jinorgbio.2008.01.031. PMID:18331758.
  10. Singh AK et al. (2008), J Mol Biol, 376, 1060-1075. Crystal structure of lactoperoxidase at 2.4 A resolution. DOI:10.1016/j.jmb.2007.12.012. PMID:18191143.
  11. Furtmüller PG et al. (2006), Arch Biochem Biophys, 445, 199-213. Active site structure and catalytic mechanisms of human peroxidases. DOI:10.1016/j.abb.2005.09.017. PMID:16288970.
  12. Jantschko W et al. (2005), Arch Biochem Biophys, 434, 51-59. Reaction of ferrous lactoperoxidase with hydrogen peroxide and dioxygen: an anaerobic stopped-flow study. DOI:10.1016/j.abb.2004.10.014. PMID:15629108.
  13. Ghibaudi E et al. (2003), Eur J Biochem, 270, 4403-4412. Unraveling the catalytic mechanism of lactoperoxidase and myeloperoxidase. PMID:14622268.

Step 1.

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Catalytic Residues Roles

Residue Roles
Asp108A covalently attached
Glu258A covalently attached
Asp108A alter redox potential
Glu258A alter redox potential
Asp110A metal ligand
Thr184A metal ligand
Phe186A metal ligand
Asp188A metal ligand
Ser190A metal ligand
His351A metal ligand
Gln105A transition state stabiliser

Chemical Components

Step 1.

Contributors

Gemma L. Holliday