Myxobolus cerebralis: identification of a cathepsin Z-like protease gene (MyxCP-1) expressed during parasite development in rainbow trout, Oncorhynchus mykiss.

Cysteine proteases are essential to the biological function of parasitic organisms and are gaining interest as the target of chemotherapeutics aimed at their control. We report a cysteine protease gene from the myxozoan Myxobolus cerebralis, the cause of whirling disease in salmonid fish. The mature gene (MyxCP-1) encodes a 248-amino acid polypeptide that includes catalytic residues similar to the papain family of cysteine proteases. MyxCP-1 features a propeptide region and sequence insertions that are characteristics of cathepsin Z proteases. Phylogenetic comparisons of M. cerebralis to other eukaryotes based on full-length cathepsin-like genes show that MyxCP-1 is the earliest lineage in the cathepsin Z group and separated from cathepsin L, B, and C-like proteases. Using TaqMan PCR differential levels of transcription of the cathepsin Z-like protease were found in earlier and later developmental stages of the parasite in experimentally infected rainbow trout (Oncorhynchus mykiss).