Mutant/mutation
In the mutant the P. berghei cpα is replaced with the complete P. falciparum cpα gene. The P. falciparum gene is under the control of the P. berghei cpα promoter region

Protein (function)
One of the few conserved actin-binding proteins of Plasmodium parasites is the F-actin capping protein (CP), which is found in all eukaryotic organisms and metazoan cell types

CP binds in a calcium-independent manner to the fast growing (barbed) ends of F-actin, thereby blocking subunit exchange. CP also belongs to the defined set of proteins that are needed to reconstitute actin-based motility in vitro.

Active CP is composed of two subunits, CPα and CPβ, and production of recombinant active CP in Escherichia coli (E. coli) is typically only achieved by co-expression of both subunits

Plasmodium CPβ is encoded by a single open reading frame, whereas CPα is composed of nine small exons. Overall, Plasmodium CPα-subunits share approximately 19% amino acid sequence identity with other eukaryotic CPα-subunits, and 50-90% identity across different Plasmodium species.

The residues that contribute to actin binding and heterodimer formation are conserved.

CPβ-subunit of rodent malaria parasite P. berghei (PbCPβ) as an essential regulator of sporozoite motility and malaria transmission. Deletion of PbCPβ did not influence asexual and sexual blood-stage development in the mammalian host. In the insect vector, Anopheles mosquitoes, mutant parasites displayed defective motility, which completely arrested life cycle progression at the sporozoite stage. It has been shown that recombinant P. berghei CPα/β heterodimers display capping activity on heterologous non-muscle actin. The stage-specific function of CPβ in sporozoites implies that CPα alone might be functional during blood infection of cpβ(-) parasites. Given that independent functions of CP subunits have not been described, this notion was unexpected and prompted to investigate the cellular role(s) of Plasmodium CPα for parasite life cycle progression.

In this study it is shown that the two CP subunits can be functionally separated. Unlike the beta subunit, the CPalpha subunit of the apicomplexan parasite Plasmodium is refractory to targeted gene deletion during blood infection in the mammalian host.

See the link F-actin-capping protein subunits for other mutants with mutated F-actin-capping protein subunits

Phenotype
The phenotype analyses indicate that P. falciparum CPα can fully complement P. berghei CPα during blood stage development.
This result also suggests that the vital CPα function(s) during blood infection are apparently conserved between the  P. berghei and  P. falciparum. Together with  biochemical  characterization of PbCPα and the previously reported successful generation of a cpβ(-) mutant parasite (RMgm-328), these genetic findings indicate that the α-subunit can operate independently of the β-subunit.

However, the mutant shows strongly reduced numbers of oocysts in A. stephensi mosquitoes and absence of salivary gland sporozites, a phenotype which is comparable to mutants lacking expression of CPβ (RMgm-328).

A P. berghei mutant in which both the cpα and cpβ genes are replaced with the complete P. falciparum cpα and cpβ genes (RMgm-1157) shows a partial rescue of the phenotype with low numbers of sporozoites present in salivar glands.

Combined these observations indicate that a functional CP heterodimer is necessary for normal oocyst and sporozoite development

Additional information

Other mutants
See the link F-actin-capping protein subunits for other mutants with mutated F-actin-capping protein subunits