A revised mechanism for how Plasmodium falciparum recruits and exports proteins into its erythrocytic host cell
Fig 8
Model of PEXEL protein targeting to the vacuolar translocon by HSP101.
(A) PEXEL-containing proteins are imported after translation into the ER via a Sec61/62/63-SPC25-PMV translocon [26] and are recognised by HSP101, either during import or after PEXEL processing, prior to their release into the ER lumen. HSP101-bound cargo is then trafficked to the parasite membrane via the vesicular trafficking system and released into the PV. HSP101 affinity for the PTEX150-EXP2 subcomplex at the vacuolar membrane drives reconstitution of the full PTEX complex capable of translocating the cargo into the host cell. The model depicted here is described for soluble PEXEL proteins, but it is possible that the same mechanism governs the trafficking of transmembrane proteins. (B) Proteins with a classical N-terminal signal sequence destined for the PV such as SERA5, are imported into the ER by the Sec61-SPC25-SPC21 complex [26]. After signal sequence cleavage, the released proteins are folded and secreted into the PV. Since these proteins are not bound to HSP101, they cannot translocate via PTEX.