Arch Biochem Biophys 1999 Jul 15;3672:173-84. doi: 10.1006/abbi.1999.1219.

The primary and higher order structures of sea urchin ovoperoxidase as determined by cDNA cloning and predicted by homology modeling.

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At fertilization, sea urchin ovoperoxidase (OPO) is incorporated into a nascent fertilization envelope in association with proteoliaisin and plays an essential role in its hardening. By cDNA cloning based on the previously reported partial amino acid sequences of Hemicentrotus pulcherrimus OPO, the cDNA and deduced amino acid sequences of the enzyme precursor were determined. Its 814-residue sequence consists of 125-residue signal- plus pro-peptides and 689-residue mature enzyme and has 92.2 and 81.4% identity with the OPOs of Strongylocentrotus purpuratus and Lytechinus variegatus, respectively. Compared with human myeloperoxidase, it has 30.3% identity and 9.6% similarity and has an additional C-terminal sequence of about 100 residues, suggesting its possible role as the site for interaction with proteoliaisin, if not for the entire sequence. The linker peptide sequence between L- and H-chains (e.g., ASFVTG and FSFFTG) cleaved off upon activation in mammalian promyeloperoxidases is intrinsically lacking in OPO, uniquely rendering the single 70K polypeptide a basic unit. The positions of distal and proximal histidines, distal arginine, and six disulfide bridges are highly conserved among mammalian and sea urchin peroxidases. The secondary structure was predicted by EMBL-PHD on the Internet for the whole sequence of mature OPO, and both secondary and tertiary structures were predicted by Swiss-Model for the partial sequences residues 18-65 and 123-570 with canine myeloperoxidase as a template. The overall architecture of the OPO molecule is close to that of human myeloperoxidase but its secondary structure has some differences based on the sequence variation, as depicted by RasMol. Another software, Swiss-PdbViewer, produced a slightly but significantly different image of the OPO structure for the same predicted atomic coordinates. A discrepancy was also found between the secondary structures of human myeloperoxidase in the PDB file and in its Swiss-PdbViewer presentation.

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Genes referenced: LOC100887844 LOC590155 op