Unexpected fold in the circumsporozoite protein target of malaria vaccines

Abstract

Circumsporozoite (CS) protein is the major surface component of Plasmodium falciparum sporozoites and is essential for host cell invasion. A vaccine containing tandem repeats, region III, and thrombospondin type-I repeat (TSR) of CS is efficacious in phase III trials but gives only a 35% reduction in severe malaria in the first year postimmunization. We solved crystal structures showing that region III and TSR fold into a single unit, an "αTSR" domain. The αTSR domain possesses a hydrophobic pocket and core, missing in TSR domains. CS binds heparin, but αTSR does not. Interestingly, polymorphic T-cell epitopes map to specialized αTSR regions. The N and C termini are unexpectedly close, providing clues for sporozoite sheath organization. Elucidation of a unique structure of a domain within CS enables rational design of next-generation subunit vaccines and functional and medicinal chemical investigation of the conserved hydrophobic pocket.

Reversible Conformational Change in the Plasmodium falciparum Circumsporozoite Protein Masks Its Adhesion Domains

“…1C). Heparin binding is attributed to the N terminus, since the thrombospondin-like type I repeat (TSR)-containing domain alone does not bind heparin (23). Further, antibodies generated against a synthetic peptide present in the N-terminal domain inhibit sporozoite invasion of hepatocytes in vitro (24), and a synthetic peptide corresponding to L 86 to G 100 blocks salivary gland invasion (25), indicating the biological importance of the N-terminal domain.…”

Biosynthesis of GDP-fucose and Other Sugar Nucleotides in the Blood Stages of Plasmodium falciparum

“…TSR domains are generally O-fucosylated in higher eukaryotes by PoFUT2, and the fucose residue can be further modified by the addition of ␤1-3 glucose (72-74). The C-terminal region of CS, containing the TSR domain, was recently expressed in HEK293T cells and structurally analyzed, showing the presence of a fucose and a glucose residue (75,76). The expression of PoFUT2 in P. falciparum (Fig.…”

Far from the Madding Crowd: the Molecular Basis for Immunological Escape ofPlasmodium falciparum

“…These cHABPs could also be sequential, a s o c c u r s w i t h T R A P c H A B P s 3 2 8 7 ( 241 TA S C G V W D E W S P Y S V 255 ) a n d 3 2 8 9 ( 251 S P C S V T Y G K G T R S R K 265 ) f o r m i n g a positively-charged trough where negativelycharged receptors bind, like heparin and HSPG (Tossavainen et al, 2006). Some others fold in such a way that they themselves can create the cavity or pocket where the cholesterol molecule b i n d s , a s o c c u r s w i t h C S P -1 4 3 9 7 ( 331 IQNSLSTEWSPCSVTCGNGI 350 ) cHABP (Doud et al, 2012) and TRAP vWA domain cHABP 3279 ( 201 FLVGCHPSDGKCNLY 215 ) (Pihlajamaa et al, 2013), unlike SPECT-1 c H A B P s 3 3 3 7 2 ( 81 A S L E E V S D H V V Q N I S KYSLT 100 ) and 33375 ( 142 TDLILKKLKKLENV NKLIKY 161 ) that, despite being on the opposite side of the molecule, form part of a cavity which has been suggested as cholesterol binding site on host cell membrane (Hamaoka and Ghosh, 2014). Some cHABPs interact with each other, s u c h a s E B A -1 4 0 c H A B P s 2 6 1 3 9 ( 441 DIASQINVNDLRGFGCNYKS 460 ), 26144 ( 541 DLADIIKGSDIIKDYYGKKM 560 ) and 26147 ( 601 LKNKETCKDYDKFQKIPQFL 620 ) as they establish an H-bond with the glycophorin C glycan 2 receptor (Lin et al, 2012) LEFT panel: Different views of three-dimensional structures of P. falciparum of the complete protein or its recombinants fragment (determined by X-ray crystallography) modelled in surfaces, displaying their corresponding cHABPs and polymorphic residues location (in pink, red and burgundy, lesser to greater polymorphism, respectively).…”

“…LEFT panel: Different views of three-dimensional structures of the complete P. falciparum protein or its recombinants fragment (determined by Xray crystallography) modelled in surfaces, displaying their corresponding cHABPs and polymorphic residues location (lesser to greater polymorphism being shown by pink, red and burgundy, respectively). (A) CSP-1 C-terminal region (PDB code 3VDK) (Doud et al, 2012) and cHABP 4397 (dark yellow) involved in binding to heparan sulphate proteoglycans (HSPGs). (B) TRAP vWA domain (PDB code 4F1J) (Pihlajamaa et al, 2013) and the location of cHABP 3271 (in dark yellow) containing the residues (in black) forming the metal ion-dependent adhesion site (MIDAS), cHABPs 3277 (in blue) and 3279 (in green) forming part of the HSPG binding site.…”

“…(Patarroyo et al, 2010;Patarroyo et al, 2012) The following part of this manuscript only deals with Spz molecules involved in invasion of hepatocytes whose 3D structures have already been determined. The relevant structures include circumsporozoite protein 1 (CSP-1) cHABP 4397 ( 331 IQNSLSTEWSPCSVTCGNGI 350 ) ( Figure 1A, dark yellow) forming a hydrophobic groove or cavity (~600 Å 3 ) where hepatocyte heparan sulphate proteoglycan (HSPG) binds (Doud et al, 2012). Spz also use the thrombospondin-related associated protein (TRAP) von Willebrand factor A-like domain (vWA) containing the metal-ion-dependent adhesion site (MIDAS) which binds Mg 2+ where cHABP 3271 ( 161 TDGIPDSYQDSLKES 175 ) has been located ( Figure 1B, dark yellow with two Mg 2+ ions in black).…”