The mucin-like, secretory type-I transmembrane glycoprotein GP900 in the apicomplexan Cryptosporidium parvum is cleaved in the secretory pathway and likely plays a lubrication role.

Cryptosporidium parvum is a zoonotic parasite and member of the phylum Apicomplexa with unique secretory organelles, including a rhoptry, micronemes and dense granules that discharge their contents during parasite invasion. The mucin-like glycoprotein GP900 with a single transmembrane domain is an immunodominant antigen and micronemal protein. It is relocated to the surface of excysted sporozoites and shed to form trails by sporozoites exhibiting gliding motility (gliding sporozoites). However, the biological process underlying its relocation and shedding remains unclear. The primary aim of this study was to determine whether GP900 is present as a transmembrane protein anchored to the plasma membrane on the surface of sporozoites and whether it is cleaved before being shed from the sporozoites. Two anti-GP900 antibodies, a mouse monoclonal antibody (mAb) to the long N-terminal domain (GP900-N) and a rabbit polyclonal antibody (pAb) to the short C-terminal domain (GP900-C), were produced for the detection of intact and cleaved GP900 proteins in sporozoites and other parasite developmental stages by microscopic immunofluorescence assay and in discharged molecules by enzyme-linked immunosorbent assay. Both anti-GP900 antibodies recognized the apical region of unexcysted and excysted sporozoites. However, anti-GP900-N (but not anti-GP900-C) also stained both the pellicles/surface of excysted sporozoites and the trails of gliding sporozoites. Both antibodies stained the intracellular meronts, both developing and developed, but not the macro- and microgamonts. Additionally, the epitope was recognized by anti-GP900-N (but not anti-GP900-C) and detected in the secretions of excysted sporozoites and intracellular parasites. GP900 is present in sporozoites and intracellular meronts, but absent in sexual stages. It is stored in the micronemes of sporozoites, but enters the secretory pathway during excystation and invasion. The short cytoplasmic domain of GP900 is cleaved in the secretory pathway before it reaches the extracellular space. The molecular features and behavior of GP900 imply that it plays mainly a lubrication role.

Li X ，Yin J ，Wang D ，Gao X ，Zhang Y ，Wu M ，Zhu G ... -  《Parasites & Vectors》

Requirement of microtubules for secretion of a micronemal protein CpTSP4 in the invasive stage of the apicomplexan Cryptosporidium parvum.

Wang D ，Jiang P ，Wu X ，Zhang Y ，Wang C ，Li M ，Liu M ，Yin J ，Zhu G ... -  《mBio》

Apical Secretory Glycoprotein Complex Contributes to Cell Attachment and Entry by Cryptosporidium parvum.

Akey ME ，Xu R ，Ravindran S ，Funkhouser-Jones L ，Sibley LD ... -  《mBio》

Characterization of a monoclonal antibody reacting with antigen-4 domain of gp900 in Cryptosporidium parvum invasive stages.

Bonnin A ，Ojcius DM ，Souque P ，Barnes DA ，Doyle PS ，Gut J ，Nelson RG ，Petersen C ，Dubremetz JF ... -  《PARASITOLOGY RESEARCH》

Identification and characterization of Cryptosporidium parvum Clec, a novel C-type lectin domain-containing mucin-like glycoprotein.

Bhalchandra S ，Ludington J ，Coppens I ，Ward HD ... -  《-》