Isolation of the salmonid rhamnose-binding lectin STL2 from spores of the microsporidian fish parasite Loma salmonae

The microsporidian parasite, Loma salmonae, is the causative agent of gill disease in both wild and netpen-reared salmonids worldwide. In this paper we report the finding of a rhamnose-binding lectin from steelhead trout, Oncorhynchus mykiss, which was found bound in high concentration to the surface coat of L. salmonae spores. SDS-PAGE, immunoblot, N-terminal sequencing and mass spectrometric analyses were used to determine that the dominant 24 kDa protein lectin observed on SDS-PAGE analysis of intact spore extracts is the O. tshawytscha variant of the previously identified rhamnose-binding lectin STL2 from rainbow trout, O. mykiss. Although the physiological role of these lectins has not been clearly delineated, they have been implicated in a variety of functions, including inhibition of pathogenic bacteria by opsonization and macrophage-mediated tumour lysis.