FASCIOLA GIGANTICA CATHEPSIN B8, AN ISOFORM PRESENT FROM METACERCARIAL TO MATURE STAGE

Thwet Oo Lwin1,2, Amornrat Geadkaew-Krenc1, Sinee Siricoon3 and Rudi Grams1

Abstract

Basic molecular and biochemical properties of a new isoform of tropical liver fluke Fasciola gigantica cathepsin B FgCB8 were analyzed. This isoform, also found in F. hepatica, most likely represents an evolutionary cathepsin B prototype in trematodes and highly conserved orthologs are present in Schistosoma mansoni and Clonorchis sinensis. F. gigantica cathepsin B FgCB1-7 form a separate clade in phylogenetic analysis and are thought to fulfill specialized roles in infection and/or nutrition processes. FgCB8 was an acidic protease with an ability to undergo auto-activation at pH 5.0 and to sustain maximal enzymatic activity at this pH value for three hours with 50% activity remaining after 24 hours. FgCB8 mRNA was detected from parasite metacercarial to mature stage as well as cecal epithelium of the latter stage. Cross-reactivity of anti-recombinant (r)FgCB8 antiserum to rFgCB5 and human cathepsin B was not detected and immune sera of experimentally-infected rabbits reacted with rFgCB8. Due to a high sequence conservation in trematodes, FgCB8 is not recommended for application as species-specific diagnostic tool.