Molecular characterization and gene expression analysis of a pattern recognition protein from disk abalone, Haliotis discus discus

Pattern recognition molecules play an important role in innate immunity by recognizing common epitopes on the surface of invading microorganism. A pattern recognition protein (PRP) was isolated from a disk abalone, Haliotis discus discus, normalized cDNA library. It encodes 420 amino acids (aa) including a 20 aa signal peptide sequence. The mature protein has an estimated molecular mass of 45 kDa and predicted pI of 5.0. The deduced aa sequence showed greatest homology (50%) with a beta-glucan recognition protein (BGRP) of the freshwater snail Biomphalaria glabrata. Characteristic potential polysaccharide binding, cell adhesion, and glucanase motifs, similar to invertebrate PRP motifs were also found in HdPRP. Reverse transcription-polymerase chain reaction (RT-PCR) results showed that the HdPRP was constitutively expressed in the gill, mantle, digestive tract, hepatopancreas and hemocytes, suggesting an innate immune role in these tissues. Animals injected with Vibrio alginolyticus bacteria showed that the mRNA expression was increased at 12 h post-injection in the gill and continued until 48 h. Abalone CuZn superoxide dismutase (HdCuZnSOD) gene expression was analyzed to detect any oxidative stress after exposure to different pathogen-associated molecular patterns (PAMP). This analysis showed that mRNA expression was significantly increased in Vibrio, lipopolysaccharides (LPS) and beta-1,3-glucan-injected animals compared to controls. Abalone PRP can recognize different PAMP and may activate different genes involved in the defence against these pathogens. It acts as an acute inducible protein that could play an important role in the abalone immune defence mechanism.