Mutant/mutation
The mutant expresses a normal ICP and a quadruple C-myc tagged version of ICP. Both icp genes are under control of the endogenous icp promoter.

ICP is conserved among numerous Plasmodium species. However, a Py-ICP ortholog had not been annotated in PlasmoDB (www.plasmodb.org). To determine if Py contained an ICP ortholog, a BLAST search of the Py genome was conducted using Pf-ICP as the query and observed highly conserved nucleotide sequences at the C-terminal region of a 7.3 kb gene, PY03424. It was found that that PY03424 was composed of two separate genes: a single exon gene is termed PY03424* and Py-ICP. The re-annotated Py-ICP gene has 85% and 34% amino acid identity to its orthologs in Pb and Pf, respectively.

Protein (function)
An endogenous cysteine protease inhibitor has been identified in P. falciparum, Pf-ICP (PF3D7_0911900; Falstatin), via a BLAST search of the Pf genome using the Trypanosoma cruzi cysteine protease inhibitor chagasin as a query. A recombinant  Pf-ICP expressed in E. coli was shown to potently inhibit a number of host proteases by in vitro protease activity assays. Additionally, Pf-ICP also inhibited several parasite proteases in these assays, including falcipain-2 and falcipain-3, but not falcipain-1. For P. berghei ICP evidence has been presented localisation in sporozoite micronemes and secretion in trails during gliding motility. Evidence has been presented that P. berghei ICP plays a role in hepatocyte invasion and is important in suppressing host cell apoptosis during liver stage development (see RMgm-396)

Phenotype
ICP is expressed in blood stages (see below for more details).
ICP-myc expressed in sporozoites Evidence is presented for a location in rhoptries.
ICP-myc expressed during liver stage development. Evidence is presented that during late liver stage development ICP is found in the host hepatocyte cytoplasm

Additional information
During ring/trophozoite stage, ICP-myc was contained within the parasite but was also partially co-localized with the PVM marker Hep17. Notably, extensions of the PV that projected into the infected erythrocyte were strongly stained for ICP and Hep17. ICP associated with vesicles within the parasite cytoplasm and also localized Py-ICP to the PV. Py-ICP was frequently associated with polymorphic exomembrane structures that appeared segregated in the infected erythrocyte cytoplasm, but might be continuous with the PVM.

Co-immunoprecipitation studies provided evidence for interaction of ICP with yoelipain-2. Epitope tagged Py-ICP consistently co-immunoprecipitated with the cysteine protease yoelipain-2 (PY00783, the ortholog of falcipain-2 and berghepain-2), and was identified by multiple peptide hits in all 5 co-immunoprecipitations. Other co-immunoprecipitated proteins included two ER-associated proteins, PY03267, the putative ortholog for Rab18 (PY01075), and two scaffolding proteins, PY05916 and PY01361.

ICP-myc expressed in sporozoites Evidence is presented for a location in rhoptries. ICP was not detected in gliding trails of sporozoites. For P. berghei ICP evidence has been presented for a micronemal location and presence in gliding trails (RMgm-396) .

During early (4 hr pi) and mid stage (24 hr pi) in vitro liver stage infection, Py-ICP-myc localized within the parasite, but was not observed outside the confines of the parasite compartment or in UIS4 positive projections of the PV. However, during late liver stage development (43 hr pi), Py-ICP was strongly detected in the host hepatocyte cytoplasm. At 2 hr pi, when liver stage parasites are still sporozoite-shaped, Py-ICP was detected inside the parasite only but not in the UIS4-positive PV. Similarly, during mid-liver stage development (16 hr and 24 hr pi), Py-ICP was distributed ubiquitously within the parasite. Py-ICP was also increasingly associated with the PV as indicated by co-localization with the PVM protein UIS4. This suggests that ICP is released into the PV but is not exported beyond the PVM. At 30 hr pi, Py-ICP appeared to be concentrated in vesicular structures that localized to the periphery of all liver stage parasites, close to the PV. A similar distribution was observed in 40% of infected cells during late liver stages (43 hr pi). However, in the majority of late liver stages at 43 hr pi (60%), Py-ICP accumulated in the cytoplasm of the infected hepatocyte, and this was associated with the partial breakdown of the PVM as indicated by discontinuous Hep17 staining

Other mutants
See RMgm-970 for successful disruption of the icp gene!!!