Bovine lactoperoxidase – a versatile one‐ and two‐electron catalyst of high structural and thermal stability

Abstract

Lactoperoxidase (LPO), a member of the peroxidase-cyclooxygenase superfamily, is found in multiple human exocrine secretions and acts as a first line of defense against invading microorganisms by production of antimicrobial oxidants. Because of its ability to efficiently catalyze one- and two-electron oxidation reactions of inorganic and organic compounds, the heme peroxidase is widely used in food biotechnology, cosmetic industry, and diagnostic kits. In order to probe its structural integrity, conformational, and thermal stability, we have undertaken a comprehensive investigation by using complementary biophysical techniques including UV-Vis, circular dichroism and fluorescence spectroscopy as well as differential scanning calorimetry (DSC). The oxidoreductase exhibits a high chemical and thermal stability under oxidizing conditions but is significantly destabilized by addition of DTT. Due to its unique ester bonds between the prosthetic group and the protein as well as six intra-chain disulfides, unfolding of the central compact (-helical core occurs concomitantly with denaturation of the heme cavity. The corresponding enthalpic and entropic contributions to the free enthalpy of unfolding are presented. Together with spectroscopic data they will be discussed with respect to the known structure of bovine LPO and homologous myeloperoxidase as well as to its practical application.

Secreted heme peroxidase from Dictyostelium discoideum: Insights into catalysis, structure, and biological role

“…5 A ). Plotting the single exponentially fitted pseudo-first order rate constants ( k obs ) versus cyanide concentration yielded an apparent second-order dissociation rate constant ( k on ) of 3.3 × 10 5 m −1 s −1 ( K D = k off / k on = 3.7 μ m ), which was ∼5-fold lower than for MPO ( k on = 1.6 × 10 6 m −1 s −1 , K D = 1.9 μ m ) and LPO ( k on = 1.3 × 10 6 m −1 s −1 , K D = 23 μ m ) ( 17 , 30 – 32 ). At pH 5.0, cyanide binding to ferric DdPoxA decreased ( k on = 8.9 × 10 4 m −1 s −1 and K D = k off / k on = 10.1 μ m ).…”

“…Similar to secreted mammalian peroxidases involved in antimicrobial activity ( 31 , 41 ) DdPoxA exhibits a high thermal stability ( T m >70 °C) in the pH range 5.0–7.0, which guarantees conformational stability under harsh conditions such as the one encountered in the soil environment of the amoeba.…”

The Significance of Lactoperoxidase System in Oral Health: Application and Efficacy in Oral Hygiene Products

“…Lactoperoxidase (both human and bovine) is a single chain, monomeric glycopeptide of approximate mass of 80,000 Da (human) or 78,000 Da (bovine) [5,14]. Each LPO molecule contains one molecule of modified autocatalytic heme B in its active center [9,15],…”

“…The mRNA analysis showed that both human and bovine LPO is composed of 712 amino acid residues and is characterized by 83% similarity, while protein analysis showed that human LPO is composed of 632 amino acid residues (including 16 cysteine residues) and a bovine one of 612 (including 15 cysteine residues) [9,15,18]. The difference between the theoretical length of the chain and the length of the analyzed protein results from the occurrence of post-translational modifications consisting of the cleavage of the propeptide and the signal peptide [13].…”

Functional Enzyme Mimics for Oxidative Halogenation Reactions that Combat Biofilm Formation

“…With regard to their active centers halogenating enzymes can be subdivided into (i) flavin‐, nonheme iron(II)‐, and S‐adenosyl‐ l ‐methionine‐dependent halogenases (F‐, NI‐, S‐HG) and (ii) cofactor‐free‐, heme iron(II)‐, or vanadium‐dependent haloperoxidases (HI‐HPO, and V‐HPO). According to the most electronegative halide that the enzymes can oxidize they are labeled chloroperoxidase (CPO, substrate Cl − , Br − , I − , e.g., myeloperoxidase in neutrophils), bromoperoxidase (BPO, substrate: Br − , I − , e.g., eosinophil peroxidase in phagocytes and lactoperoxidase in human exocrine secretions), and iodoperoxidase (substrate: I − , e.g., thyroid peroxidase). The highly reactive intermediates, e.g., hypohalous acids (HOX, X = Cl, Br, I, CN, SCN), react subsequently with different nucleophilic acceptors (R‐H) to form a variety of halogenated metabolic compounds (R‐X, X = (pseudo‐) halogen, Equations and ).…”