An antibacterial V V11 kDa protein designated chlamysin was isolated from viscera of the marine bivalve Chlamys islandica. Chlamysin inhibited the growth of all Grampositive and Gram-negative bacteria tested. The isolated protein was highly efficient in hydrolyzing Micrococcus luteus cells only at low pH (4.5^6.2) and at low temperature (4^35³C). No significant loss of enzyme activity was observed after 30 days storage at room temperature or after heating to 70³C for 15 min, suggesting relatively high protein structure stability. Sequenceanalyzed fragments of the protein revealed data which guided the isolation of the cDNA gene, encoding a 137 amino acid chlamysin precursor in scallops. The deduced protein contains a high portion of cysteine, serine and histidine residues and has a predicted isoelectric point below 7. The chlamysin protein was found to have sequence homology to an isopeptidase and to a recently published bivalve lysozyme.z 1999 Federation of European Biochemical Societies.

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BackgroundWe have previously isolated a thermolabile nuclease specific for double-stranded DNA from industrial processing water of Northern shrimps (Pandalus borealis) and developed an application of the enzyme in removal of contaminating DNA in PCR-related technologies.Methodology/Principal FindingsA 43 kDa nuclease with a high specific activity of hydrolysing linear as well as circular forms of DNA was purified from hepatopancreas of Northern shrimp (Pandalus borealis). The enzyme displayed a substrate preference that was shifted from exclusively double-stranded DNA in the presence of magnesium to also encompass significant activity against single-stranded DNA when calcium was added. No activity against RNA was detected. Although originating from a cold-environment animal, the shrimp DNase has only minor low-temperature activity. Still, the enzyme was irreversibly inactivated by moderate heating with a half-life of 1 min at 65°C. The purified protein was partly sequenced and derived oligonucleotides were used to prime amplification of the encoding cDNA. This cDNA sequence revealed an open reading frame encoding a 404 amino acid protein containing a signal peptide. By sequence similarity the enzyme is predicted to belong to a family of DNA/RNA non-specific nucleases even though this shrimp DNase lacks RNase activity and is highly double-strand specific in some respects. These features are in agreement with those previously established for endonucleases classified as similar to the Kamchatka crab duplex-specific nuclease (Par_DSN). Sequence comparisons and phylogenetic analyses confirmed that the Northern shrimp nuclease resembles the Par_DSN-like nucleases and displays a more distant relationship to the Serratia family of nucleases.Conclusions/SignificanceThe shrimp nuclease contains enzyme activity that may be controlled by temperature or buffer compositions. The double-stranded DNA specificity, as well as the thermolabile feature, strengthens its potential for in vitro applications.