Essential sporozoite protein (PubMed:29554084, PubMed:32150583). In the mosquito vector, required for sporozoite development in the oocyst, migration through the vector hemolymph and entry into the vector salivary glands (By similarity). In the vertebrate host, required for sporozoite migration through the host dermis and infection of host hepatocytes (PubMed:29554084, PubMed:32150583). Binds to highly sulfated heparan sulfate proteoglycans (HSPGs) on the surface of host hepatocytes (By similarity). In the vertebrate host, binds to highly sulfated heparan sulfate proteoglycans (HSPGs) on the surface of host hepatocytes and is required for sporozoite invasion of the host hepatocytes. Localizes to the cytoplasm and the cell membrane in oocysts at day 6 post infection and then gradually distributes over the entire cell surface of the sporoblast and the budding sporozoites. The N-terminus is involved in the initial binding to heparan sulfate proteoglycans (HSPGs) on the surface of host hepatocytes (PubMed:27560376). The N-terminus masks the TSP type-1 (TSR) domain which maintains the sporozoites in a migratory state, enabling them to complete their journey to the salivary gland in the mosquito vector and then to the host liver. The unmasking of the TSP type-1 (TSR) domain when the sporozoite interacts with the host hepatocyte also protects sporozoites from host antibodies (By similarity). The TSP type-1 (TSR) domain is required for sporozoite development and invasion. CSP has two conformational states, an adhesive conformation in which the TSP type-1 (TSR) domain is exposed and a nonadhesive conformation in which the TSR is masked by the N-terminus. TSR-exposed conformation occurs during sporozoite development in the oocyst in the mosquito vector and during host hepatocyte invasion. TSR-masked conformation occurs during sporozoite migration through the hemolymph to salivary glands in the mosquito vector and in the host dermis. The GPI-anchor is essential for cell membrane localization and for sporozoite formation inside the oocyst. During host cell invasion, proteolytically cleaved at the cell membrane in the region I by a papain-like cysteine protease of parasite origin (By similarity). Cleavage is triggered by the sporozoite contact with highly sulfated heparan sulfate proteoglycans (HSPGs) present on the host hepatocyte cell surface (By similarity). Cleavage exposes the TSP type-1 (TSR) domain and is required for productive invasion of host hepatocytes but not for adhesion to the host cell membrane (By similarity). Cleavage is dispensable for sporozoite development in the oocyst, motility and for traversal of host and vector cells (By similarity). O-glycosylated; maybe by POFUT2. The sequence of the repeats varies across Plasmodium species and strains. CSP immunodominant B cell epitopes are primarily located in the central repeats (PubMed:29554084). Antibodies against CSP and particularly against the central repeats can neutralize infection at the pre-liver stage and thus makes CSP an attractive candidate for the development of vaccines (PubMed:29554084, PubMed:32150583). Belongs to the plasmodium circumsporozoite protein family.