Molecular interactions involved in red cell invasion by malaria parasites

Abstract

braneThe transmembrane topology of eukaryotic integral membrane proteins is in most cases determined during the insertion of the nascent polypeptide into the ER membrane. We have used engineered glycosylation sites to study how individual transmembrane segments control topology, the kinetics of membrane insertion, and the formation of 'helical hairpins' of closely spaced pairs of transmembrane helices. From this and other work it is becoming increasingly clear that a precise interplay between topological determinants in the nascent polypeptide and the translocon is critical for proper membrane protein assembly. MonnC, M., Hermansson, M., and von Heijne, G. (1999) A turn propensity scale for transmembrane helices. J.Mol.Bio1. 288:141. MonnC, M., Nilsson, IM., Elofsson, A., and von Heijne, G. (1 999) Turns in transmembrane helices: Determination of the minimal length of a "helical hairpin" and derivation of a finegrained turn propensity scale. J. Mol. Biol. 293:807. Nilsson, IM., Witt, S., Kiefer, H., Mingarro, I., and von Heijne, G. (2000) Distant downstream sequence determinants can control N-tail translocation during protein insertion into the ER membrane. J.Biol.Chem. 275:6207.SecA, the dimeric ATPase subunit of bacterial protein translocase, catalyzes translocation through ATP-driven membrane cycling at SecYEG. We show that the SecA protomer comprises two structural modules: the ATPase N-domain, containing the high affinity nucleotide binding site NBDl and the regulatory C-domain. The C-domain binds to the N-domain in each protomer and to the Cdomain of another protomer to form SecA dimers. NBDl is necessary and sufficient for low level, independent ATP hydrolysis. However, multiple ATP turnovers at NBDl are regulated by two Intra molecular Regulators of ATP hydrolysis (IRA elements): IRA2 on the N-domain that contains conserved DEAD helicase motifs and IRA1, a highly conserved sequence unique to the SecA proteins and located in the C-domain.Both IRA elements act through defined intra domain interactions and fine-tune ATP hydrolysis at NBD1. Furthermore, IRAl mediates N-/C-domain binding and acts as a molecular switch: it suppresses ATP hydrolysis in cytoplasmic SecA, while it releases hydrolysis in SecY-bound SecA during translocation. Both IRA elements are essential for protein translocation and life. We propose that conserted action of IRAl and IRA2 couples ATP binding and hydrolysis to SecA membrane insertion/deinsertion cycles and lead to substrate translocation, by controlling nucleotide-regulated relative motions between the N-/C-domains. The invasion of red cells by malaria parasites is mediated by a series of molecular interactions between host receptors and parasite ligands.Plasmodium v i v a and P. knowlesi require interaction with the Duffy blood group antigen for invasion of human erythrocytes. P. knowlesi invades rhesus monkey erythrocytes by multiple pathways using the Duffy antigen as well as alternate receptors. P. falciparum commonly uses sialic acid residues on glycophorin A as invasion rece...