Molecular characterization and immune analysis of a defensin from freshwater pearl mussel, Hyriopsis schlegelii

Article history:Received 5 November 2011Received in revised form 21 December 2011Accepted 22 December 2011Available online 4 January 2012Keywords:Freshwater musselHyriopsis schlegeliiDefensinmRNA expressionImmune response Defensin is one of the most important antimicrobial peptides(AMPs) in bivalves and is involved in the im-mune responses. Herein, we reported the isolation and initial characterization of a defensin from the fresh-water pearl mussel, Hyriopsis schlegelii (designated as Hs-defn) and its immune response for the first time.The full length Hs-defn cDNA was 410 bp long and consisted of a 51 bp 5'UTR, a 161 bp 3'UTR with amRNA instability motif (AATAAA) and an open reading frame(ORF) of 198 bp encoding a polypeptide of 65amino acids. The deduced amino acid sequence of Hs-defn shared certain common features of AMPs, suchas α-helical structure, net positive charge, lower molecular mass and high hydrophobic residue ratio. Homo-logue searching against GenBank database suggested that Hs-Defn was also phylogenetically close to thedefensin isoforms identified from other mollusks. Furthermore, predicted with homology-modeling method,the three-dimensional structureofHs-Defndemonstrated a significantsimilaritywith otherknown defensinssuch as oyster C. gigas and insect P. terraenovae defensins. Phylogenetic analysis results further revealed thatHs-defn is a member of invertebrate defensin family.Results of tissue specific analysis showed that the expression level of Hs-defn mRNA was the highest in hae-mocytes, moderate in gill, hepatopancrease, mantle and intestine, the lowest in foot, adductor muscle, gonadand kidney. After pathogenic Aeromonas hydrophila stimulation, the Hs-defn mRNA expression was signifi-cantly up-regulated at2 hand12 hin haemocytes, gill, mantle andhepatopancrease. These resultsimplicatedthat Hs-Defn was a constitutive and inducible acute-phase protein which was perhaps involved in the im-mune defense of pearl mussel.© 2011 Elsevier B.V. All rights reserved.