Mutant/mutation
The mutant lacks expression of ECP1 (egress cysteine protease 1; PbSERA5, an ortholog of P. falciparum SERA8).

Protein (function)
The ECP1 protein belongs to a family of proteases that were termed serine repeat antigens (SERAs). Members of this distinct Plasmodium protease family  belong to papain-like cysteine proteases based on a central 30-kD protease domain. A hallmark of papain-family cysteine proteases is the presence of the catalytic triad with invariant cysteine, histidine, and asparagine residues and the oxyanion-hole glutamine residue. Presence of these residues in the ECP1 proteins indicates that they might function as proteases.

Plasmodium species possesses SERAs of two major groups, specified as 'cysteine-type SERAs' and 'serine-type SERAs'. Serine-type SERAs contain an active site serine residue instead of the canonical cysteine residue. The genomes of different Plasmodium species contain different numbers of SERA genes. P. falciparum possesses nine SERA protease genes whereas the P. berghei genome contains five. P. falciparum possesses six “serine-type” (SERA1 to SERA5 and SERA9) and three “cysteine-type” (SERA6 to SERA8) SERAs. In P. falciparum mutants have been generated lacking expression of SERA1, 2, 3, 4 , 7, 8 and 9 without a distinct phenotype in the blood stages (MvCoubrie J.E. et al,  2007, Infection and Immunity, 75:5565-74).

SERA genes of P. berghei are arranged in a tandem cluster that contains two serine-type SERAs (PbSERA1, -2) and three cysteine-type SERAs (PbSERA3, -4 and -5). 

Sequence homology and syntenic organisation indicate that PbSERA3, -4 (PB000352.01.0) and -5 (PB000649.01.0) are orthologs of P. falciparum SERA6, -7, -8.

Phenotype
The phenotype analyzes indicate a role of ECP1 in egress of mature, viable sporozoites from the mature oocysts. In addition, it may play a role during liver stage development since the oocyst-derived sporozoites were not infectious to the mammalian host.

Additional information
Although the substrate of ECP1 is not known yet, the phenotype analysis of the mutant suggests that CSP is a likely candidate for a direct or indirect downstream proteolytic processing event, particularly because it seems to be one of the dominant parasite-derived components lining the inner side of the oocysts. See alo mutant RMgm-68  which expresses a mutated form of CS (region II-plus). Sporozoites of this mutant also show a defect in egress from the oocyst.

Other mutants

Other mutants
RMgm-271: A mutant expressing GFP under the control of the 5'-UTR of PbSERA3 (an ortholog of P. falciparum SERA6)
RMgm-272: The mutant expresses in addition to the endogenous SERA3  (the ortholog of P. falciparum SERA6) a TAP-tagged form of SERA3 under control of its own 5'-UTR and the dhfr/ts 3'-UTR
RMgm-365: A mutant expressing the endogenous SERA1 protein fused to the mCherry red fluorescent protein
RMgm-366: A mutant expressing the endogenous SERA2 protein fused to the mCherry red fluorescent protein
RMgm-367: A knock-out mutant lacking expression of SERA1
RMgm-368: A knock-out mutant lacking expression of SERA2
RMgm-369: A double knock-out mutant lacking expression of SERA1 and SERA2