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Spectroscopic and binding studies on the stereoselective interaction of tyrosine with horseradish peroxidase and lactoperoxidase.

ABSTRACT: The interaction of a series of derivatives of tyrosine with horseradish peroxidase (HRP) and lactoperoxidase (LPO) was studied by using optical difference spectroscopy, c.d. and proton n.m.r. spectroscopy in order to reveal differences in the mode of binding of L-tyrosine and D-tyrosine, which are substrates of but react at different rates with the two peroxidases, to HRP and LPO. All the donor molecules form 1:1 complexes with HRP and LPO, but they display a range of affinities for the enzymes. Whereas D-tyrosine binds to HRP more strongly than does L-tyrosine, the opposite holds for the binding to LPO. The distances of the protons of bound tyrosine molecules from the haem iron atoms of HRP and LPO indicate that the site of binding of these substrates is the same as that of simple phenols. This involves the interaction of the phenol nucleus with a protein tyrosine residue [Sakurada, Takahashi & Hosoya (1986) J. Biol. Chem. 261, 9657-9662; Modi, Behere & Mitra (1989) Biochim. Biophys. Acta 996, 214-225]. However, for the present substrates the additional interaction of the carboxylate group with a protein residue (probably an arginine residue) provides further stabilization for the adducts HRP-D-tyrosine and LPO-L-tyrosine with respect to the corresponding complexes with the opposite enantiomers. The differences in the mode of binding of L-tyrosine and D-tyrosine to HRP and LPO is thus determined by the fact that the spatial arrangement of the interacting protein residues can recognize the chirality of the C(alpha)-CO2- and C(beta)-C6H4OH attachment bonds of the substrates.

SUBMITTER: Casella L

PROVIDER: S-EPMC1151572 | biostudies-other | 1991 Oct

REPOSITORIES: biostudies-other

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Project description:BACKGROUND: Horseradish peroxidases (HRPs) from Armoracia rusticana have long been utilized as reporters in various diagnostic assays and histochemical stainings. Regardless of their increasing importance in the field of life sciences and suggested uses in medical applications, chemical synthesis and other industrial applications, the HRP isoenzymes, their substrate specificities and enzymatic properties are poorly characterized. Due to lacking sequence information of natural isoenzymes and the low levels of HRP expression in heterologous hosts, commercially available HRP is still extracted as a mixture of isoenzymes from the roots of A. rusticana. RESULTS: In this study, a normalized, size-selected A. rusticana transcriptome library was sequenced using 454 Titanium technology. The resulting reads were assembled into 14871 isotigs with an average length of 1133 bp. Sequence databases, ORF finding and ORF characterization were utilized to identify peroxidase genes from the 14871 isotigs generated by de novo assembly. The sequences were manually reviewed and verified with Sanger sequencing of PCR amplified genomic fragments, resulting in the discovery of 28 secretory peroxidases, 23 of them previously unknown. A total of 22 isoenzymes including allelic variants were successfully expressed in Pichia pastoris and showed peroxidase activity with at least one of the substrates tested, thus enabling their development into commercial pure isoenzymes. CONCLUSIONS: This study demonstrates that transcriptome sequencing combined with sequence motif search is a powerful concept for the discovery and quick supply of new enzymes and isoenzymes from any plant or other eukaryotic organisms. Identification and manual verification of the sequences of 28 HRP isoenzymes do not only contribute a set of peroxidases for industrial, biological and biomedical applications, but also provide valuable information on the reliability of the approach in identifying and characterizing a large group of isoenzymes.

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Spectroscopic and binding studies on the stereoselective interaction of tyrosine with horseradish peroxidase and lactoperoxidase.

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