Mutant/mutation
In the mutant (CS^5M) the wild type cs gene is replaced with a mutated cs gene carrying 5 mutations that changed the natural H-2K^d restricted epitope SYIPSAEKI to SIINFEKL, an H-2K^b restricted epitope

Protein (function)
The CS protein is the major protein on the surface of sporozoites and is critical for development of sporozoites within the oocysts and is involved in motility and invasion of both the salivary gland of the mosquito and the liver cells. The protein is also found on the oocyst plasma membrane and on the inner surface of the oocyst capsule. Specific motifs in CS are involved in sporozoite binding to mosquito salivary glands and in sporozoite attachment to heparan sulfate proteoglycans in the liver of the mammalian host. During substrate-dependent locomotion of sporozoites, CS is secreted at the sporozoite anterior pole, translocated along the sporozoite axis and released on the substrate at the sporozoite posterior pole. Following sporozoite invasion of hepatocytes, the CS is released in the host cell cytoplasm.

Phenotype
See additional information below

Additional information
Phenotype analyses of sporozoites of the mutant (CS^5M), expressing a mutated CS protein with the H-2K^b epitope SIINFEKL, provide evidence that both dendritic cells (DCs) and hepatocytes CS epitopes must reach the cytosol and use the TAP transporters to access the ER.
In addition evidence is presented that in DCs, CS is cross-presented via endosomes while, conversely, in hepatocytes the CS protein must be secreted directly into the cytosol. These observations suggests that the main targets of protective CD8+ T cells are parasite proteins exported to the hepatocyte cytosol.
Secretion of the CS protein into hepatocytes was not dependent upon parasite-export (Pexel/VTS) motifs in this protein (see also mutant RMgm-614).

In the CS^5M mutant the epitope SIINFEKL is inserted in place of a well-defined natural epitope, leaving intact the neighboring residues to ensure correct proteasomal processing, thus the model epitope is presented exactly as the natural CS epitope. This makes this mutant an useful system in which to study antigen processing and presentation. Therefore, the authors anticipate that the CS^5M mutant will be a powerful tool for use in future studies of antigen specific immune responses to malaria sporozoites.

Other mutants
RMgm-614: A mutant expressing a mutated CS containing the model SIINFEKL H-2K^b restricted epitope with additional mutations of the Pexel/VTS motifs