Molecular characterization of goose- and chicken-type lysozymes in emu ( Dromaius novaehollandiae): Evidence for extremely low lysozyme levels in emu egg white

Lysozyme (LZ), a bacteriolytic enzyme, is found in the egg white of many avian eggs and plays an important role in host defense; however, LZ activity in emu ( Dromaius novaehollandiae) egg white is exceptionally undetectable. We cloned and characterized emu goose-type LZ (LZG) and chicken-type LZ (LZC) genes. RT-PCR analysis revealed very low LZG gene expression levels and absence of LZC gene expression in the emu oviduct. Sequencing of full-length LZG and LZC cDNAs indicated that their amino acid sequences show high similarities to ostrich LZG and LZC, respectively, with conserved catalytic residues for enzymatic activities. Whereas recombinant emu LZG prepared using Pichia pastoris exhibited similar enzyme activity as ostrich LZG, recombinant emu LZC exhibited significantly higher lytic activity than chicken LZC. We concluded that emus have functional genes for both LZG and LZC like many other avians, and the LZG gene is expressed in oviduct probably as in other ratite, however, its expression levels in egg white were low to be detected. ► Lysozyme was substantially undetectable in emu egg white. ► Emu had goose- and chicken-type lysozyme genes. ► The sequences showed high similarity to those of ostrich and chicken lysozymes. ► Gene expression for goose-type lysozyme was very low level in emu oviduct. ► Enzyme activities of recombinant lysozymes proved those genes are functional.