Mantle tissue extracts from the Pacific oyster, Crassostrea gigas, exhibited anti-Gram-positive bacterial and lysozyme activities over a wide pH range, suggesting that multiple defensive mantle lysozymes were present. Degenerated reverse-transcription PCR detected the expression of two mantle lysozymes, CGL-1 and a novel lysozyme CGL-3, confirming the presence of multiple lysozymes in the mantle. Since CGL-3 is a cognate protein of the digestive lysozyme CGL-2, it is assumed that CGL-3 has evolved specifically a defensive function. Functional assays using recombinant CGL-1 and CGL-3 suggested that CGL-1 and CGL-3 play a major defensive role in the mantle tissue, and that they are responsible for lysozyme activity under different pH, ionic strength and temperature conditions. Based on these observations, we conclude that multiple mantle lysozymes in the Pacific oyster are better for host-defense under broader conditions than a single lysozyme.
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