N-terminal processing of proteins exported by malaria parasites

Abstract

Malaria parasites utilize a short N-terminal amino acid motif termed the Plasmodium export element (PEXEL) to export an array of proteins to the host erythrocyte during blood stage infection. Using immunoaffinity chromatography and mass spectrometry, insight into this signalmediated trafficking mechanism was gained by discovering that the PEXEL motif is cleaved and N-acetylated. PfHRPII and PfEMP2 are two soluble proteins exported by Plasmodium falciparum that were demonstrated to undergo PEXEL cleavage and N-acetylation, thus indicating that this Nterminal processing may be general to many exported soluble proteins. It was established that PEXEL processing occurs upstream of the brefeldin A-sensitive trafficking step in the P. falciparum secretory pathway, therefore cleavage and N-acetylation of the PEXEL motif occurs in the endoplasmic reticulum (ER) of the parasite. Furthermore, it was shown that the recognition of the processed N-terminus of exported proteins within the parasitophorous vacuole may be crucial for protein transport to the host erythrocyte. It appears that the PEXEL may be defined as a novel ER peptidase cleavage site and a classical N-acetyltransferase substrate sequence.

Profile of Michael A. Marletta

“…Marletta used spectroscopy to study the heme-binding site of HRP-2 and the molecular nature of the heme-HRP2 interaction (19). In another study with UCSF molecular biologist Joseph DeRisi and others, Marletta showed that a highly conserved, five-amino acid signal sequence in the N terminus of HRP2, called PEXELPlasmodium export element-undergoes enzymatic cleavage and acetylation in the parasite's endoplasmic reticulum before the parasite exports the protein to human erythrocytes (20).…”

In Silico Characterization of Plasmodium falciparum and P. yoelii Translocon and Exoribonuclease II (RNase II) Identified in the Merozoite Rhoptry Proteome

“…The gene has six orthologs in PlasmoDB [18]. PTEX150 is part of a Plasmodium transport protein complex comprising PEXEL, PTEX88, EXP2 and HSP70 [23,38,39]. PTEX150 has a putative endoplasmic reticulum (ER) signal sequence that is found in most species of Plasmodium that infect humans and in Theileria, another member of the apicomplexan phylum [39].…”

“…The RNAse II and translocon genes were amplified by polymerase chain reaction (PCR) from Plasmodium genomic DNA using primers designed from DNA sequences obtained from PlasmoDB [18] for use in recombinant DNA construction. Due to the differences observed in localization of proteins involved in parasitophorous vacuole membrane (PVM) transport and exported proteins [23][24][25], gene mining approaches and bioinformatics were employed to examine data present in PlasmoDB [18], regarding gene and protein annotations for P. falciparum genes PF3D7_0906000 and PF3D7_1436300. Predicted structural characteristics, functional domains and motifs from annotated data within the PlasmoDB [18] database were compared, in an attempt to develop testable experimental approaches that can identify specific conserved features that will expand our understanding of asexual stage host cell invasion and parasitism, identify new vaccine and drug targets and new diagnostic biomarkers.…”

Maurer's clefts, the enigma of Plasmodium falciparum

“…That amount represents nearly 10% of all genes present in P. falciparum (46,47,68,86). Upon export the PEXEL motif is processed in the ER by plasmepsin V (87, 88), with a subsequent N-terminal acetylation (89,90), and possibly involving binding of phosphatidylyinositol-3-phosphate [PI(3)P] to the PEXEL (91). Export into the parasitophorous vacuole is via vesicular traffic, but how proteins destined for the host cytosol are sorted beyond the plasma membrane remains speculative (89,92,93).…”