Research Article: Characterization and phylogenetic analysisof a g-type lysozyme gene variant from the skin mucus of grass carp (Ctenopharyngodon idella)

The g-type lysozyme is one of the three major diverse lysozyme types recognized in the animal kingdom including fish. Using the RT-PCR technique, a ۵۵۵ bp cDNA fragment encoding a g-type lysozymewas isolated from the skin mucus of Ctenopharyngodon idella using homolog primes. The cDNA named Ci-Kh, codes for ۱۸۵ amino acids with a predicted molecular weight of ۲۰.۴۹ kDa and theoretical pI of ۹.۱۳. The sequence consists of one cysteine residue with no predicted signal peptide. Domain analysis showed e-value of ۳.۷۴e-۱۰۷ with the conserved domain of lysozyme-like superfamily (cd۰۱۰۲۱) between amino acid residues ۱۲ to ۱۸۴. Multiple alignment with the lysozyme genes from other fish species revealed that this protein have a goose egg white lysozyme (GEWL) domain containing two conserved catalytic residues (Glu۷۳ and Asp۹۷) and N-acetyl-D-glucosamine binding site (Glu۷۳, Asp۸۵, Asp۹۷, Tyr۱۰۰, His۱۰۱, His۱۰۲, Ile۱۱۹, Tyr۱۴۷, Asn۱۴۸). Protein structure prediction software revealed a prediction of ۵۸% and ۴۲% of a-helical and random coils for the coding sequence of Ci-Kh, respectively.The ۳D model of Ci-Kh revealed that this protein was mainly composed of five main helices and random coils. Phylogenetic analysis indicated that Ci-Kh matched the group of five grass carp g-type lysozyme transcript variants with ۸۶-۹۹% similarity. Among the five variants of this gene, Ci-Kh sequence had the highest and lowest genetic distance with C. idella variant X۲ (۸.۶%) and X۳ (۱.۱%) sequences, respectively. We conclude that Ci-Kh as a different variant of g-type lysozyme cannot be ruled out.

کلیدواژه ها:

G-type lysozyme ، Skin mucus ، Ctenopharyngodon idella