2. Plasmodium parasites appear to require P2 on the infected red
cell surface at the trophozoite/early schizogonic stage
During the late trophozoite/early schizogonic stage, SDS resistant P2
oligomers have been localized on the surface of iRBCs (Das et al.,
2012a). Blocking the accessibility of oligomeric P2 on the iRBCs surface
using highly specific monoclonal antibodies resulted in nuclear division
arrest of the parasite (Das et al., 2012a). In the arrested parasites,
the blockage of import of fluorescently labeled lipid molecule, FM4-64
has been observed may be as a consequence of the degradation of lipid
importing structures called tubovesicular network (TVN) (Das et al.,
2012a; Lauer et al., 1997; Haldar et al., 2001; Tames et al., 2008).
Washing off antibodies from the P. falciparum culture medium
resulted in the reformation of TVN structures, the continuation of
parasite nuclear division, and the completion of schizogonic processes
of arrested parasites (Das et al., 2012a), indicating a potential
non-ribosomal role (s) of oligomeric P2 protein on the iRBCs surface.
The P2 oligomers on iRBCs surface appear to be SDS resistant homo/hetero
tetrameric in nature (Das et al., 2012a; Das et al., 2012b) which did
not resolve to a monomer in SDS containing reducing polyacrylamide gels,
however, contrary to the iRBC surface, P2 protein in the parasite
cytoplasm is predominantly present as a monomer indicating a possible
role of SDS resistant oligomerization and oligomeric form of P2 on iRBC
surface at trophozoite stage of parasite growth. Hence oligomeric P2 on
the iRBCs surface appears to be required for the progression of the
parasite growth and development. The indispensability was further
confirmed as the P2 gene was found to be refractory to deletion in
Plasmodium berghei (Das et al., 2012a; Bushell et al., 2017) and
recently shown in Plasmodium falciparum (Zhang et al., 2018).
Apart from the iRBC surface, P2 protein has also been localized on the
surface of Plasmodium falciparum (Pf) and tachyzoite surface ofToxoplasma gondii (Tg) as either monomer or as an oligomer and
have been implicated for host cell invasion using growth inhibition
assay (GIA) (Sudarsan et al., 2015).