Authors

Discussion

Trypanosoma brucei spp. develop into mammalian-infectious metacyclic trypomastigotes inside the tsetse salivary glands.  Besides acquiring a variant surface glycoprotein (VSG) coat, little is known about the expression of invariant surface antigens by the metacyclic stage.  Proteomics analyses of saliva from T. brucei-infected flies identified, in addition to VSG and Brucei Alanine-Rich Protein (BARP) peptides, a family of GPI-anchored surface proteins herein named Metacyclic Invariant Surface Proteins (MISP).  The MISP family is encoded by five paralog genes with >80% protein identity, which are exclusively expressed by salivary gland stages of the parasite, and peaks in metacyclic stage as shown by confocal microscopy and immuno-high resolution scanning electron microscopy.  Crystallographic analysis of MISP and a high confidence model of BARP reveal a triple helical bundle architecture commonly found in other trypanosome surface proteins.  Molecular modelling combined with live fluorescent microscopy suggests that MISP expose immunogenic N-terminal epitopes above the VSG coat, although vaccination with a recombinant MISP isoform did not protect mice against a T. brucei infectious bite.  Lastly, both using RNAi and CRISPR-Cas9-driven knock out of all MISP paralogues suggests they are not essential for parasite development in the tsetse vector.