Molecular cloning, genomic structure and antimicrobial activity of PtALF7, a unique isoform of anti-lipopolysaccharide factor from the swimming crab Portunus trituberculatus

► A unique ALF isoform (PtALF7) from Portunus trituberculatus was cloned. ► PtALF7 shared high similarity with PtALF1-3 but low with PtALF4-6. ► Totally 128 SNPs were detected in PtALF7 gene. ► PtALF7 transcript was predominantly expressed in hemocytes. ► The recombinant PtALF7 showed broad spectrum antibacterial activity.