A β-defensin isoform from the Flathead grey mullet, Mugil cephalus (Linnaeus 1758): Structural and functional characterisation in silico

Defensins are an important class of AMPs, rich in cysteine with antibacterial, antifungal and antiviral functions. The present study identified and functionally characterised a β-defensin gene from Grey mullet, Mugil cephalus, termed as Mc-Def. A 192 base pair complementary DNA with an open reading frame encoding 63 amino acids comprising 20 amino acid signal and 43 amino acid mature peptide region was obtained. Mc-Def has a net charge of 3.9 and a molecular weight of 7.27 kDa with an isoelectric point of 8.88. It possessed six cysteines forming 3 disulphide bonds between C¹–C⁵, C²–C⁴ and C³–C⁶. Three dimensional structure identified a short N-terminal α helix followed by β sheet strands stabilized by disulfide bonds. The mRNA structure was predicted by Biomodel server with significant MEF score. Multiple sequence alignment and phylogeny revealed the sequence similarity of Mc-Def with fish β-defensin 2 type of AMPs. Molecular diversity and evolution of β-defensin provided immunity to host system against various infections. In silico analysis identified its potential as antibacterial, antifungal, anticancer, antioxidant and non-hemolytic peptide activity. These intriguing results firmly suggest that the Mc-Def can be used as a potent drug molecule in fish health management.