Isolation, cDNA Cloning, and Structure-based Functional Characterization of Oryctin, a Hemolymph Protein from the Coconut Rhinoceros Beetle, Oryctes rhinoceros, as a Novel Serine Protease Inhibitor

• Published in: The Journal of biological chemistry 2010-09, Vol.285 (39), p.30150-30158
• Main Authors: Horita, Shoichiro, Ishibashi, Jun, Nagata, Koji, Miyakawa, Takuya, Yamakawa, Minoru, Tanokura, Masaru
• Format: Article
• Language: English
• Subjects: Animals; Cloning, Molecular; Coleoptera - chemistry; Coleoptera - genetics; Disulfide; DNA, Complementary - genetics; Enzymology; Hemolymph - chemistry; Insect; Insect Proteins - chemistry; Insect Proteins - genetics; Insect Proteins - isolation & purification; NMR; Nuclear Magnetic Resonance, Biomolecular; Oryctes rhinoceros; Peptide Conformation; Protease Inhibitor; Protein Structure; Protein Structure and Folding; Protein Structure, Secondary; Protein-Protein Interactions; Serine Protease; Serine Proteases - chemistry; Serine Proteinase Inhibitors - chemistry; Serine Proteinase Inhibitors - genetics; Serine Proteinase Inhibitors - isolation & purification; Structure-Activity Relationship
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M110.124735

We isolated oryctin, a 66-residue peptide, from the hemolymph of the coconut rhinoceros beetle Oryctes rhinoceros and cloned its cDNA. Oryctin is dissimilar to any other known peptides in amino acid sequence, and its function has been unknown. To reveal that function, we determined the solution structure of recombinant 13C,15N-labeled oryctin by heteronuclear NMR spectroscopy. Oryctin exhibits a fold similar to that of Kazal-type serine protease inhibitors but has a unique additional C-terminal α-helix. We performed protease inhibition assays of oryctin against several bacterial and eukaryotic proteases. Oryctin does inhibit the following serine proteases: α-chymotrypsin, endopeptidase K, subtilisin Carlsberg, and leukocyte elastase, with Ki values of 3.9 × 10−10m, 6.2 × 10−10m, 1.4 × 10−9m, and 1.2 × 10−8m, respectively. Although the target molecule of oryctin in the beetle hemolymph remains obscure, our results showed that oryctin is a novel single domain Kazal-type inhibitor and could play a key role in protecting against bacterial infections.