Zoonotic Cryptosporidium Parasites Possess a Unique Carbohydrate-binding Protein (Malectin) that is Absent in other Apicomplexan Lineages

Abstract

Malectin is a carbohydrate-binding protein that binds Glc(2)- N -glycan and is present in animals and some alveolates. This study aimed to characterize the general molecular and biochemical features of Cryptosporidium parvum malectin (CpMal). Polyclonal antibodies were raised for detecting native CpMal by western blotting and immunofluorescence assays. Recombinant CpMal and human malectin (HsMal) were produced, and their binding activities to amylose and the host cell surface were compared. Far-western blotting and far-immunofluorescence assays were used to detect potential binding partners of CpMal in the parasite. Native CpMal appeared to exist in dimeric form in the parasite and was distributed in a diffuse pattern over sporozoites but was highly concentrated on the anterior and posterior sides near the nuclei. CpMal, compared with HsMal, had significantly lower affinity for binding amylose but substantially higher activity for binding host cells. Recombinant CpMal recognized three high molecular weight protein bands and labeled the sporozoite posterior end corresponding to the crystalloid body, thus suggesting the presence of its potential ligands in the parasite. Two proteins identified by proteomics should be prioritized for future validation of CpMal-binding. CpMal notably differs from HsMal in molecular and biochemical properties; thus, further investigation of its biochemical and biological roles is warranted.