Structural basis of epitope selectivity and potent protection from malaria by PfCSP antibody L9

Abstract

A primary objective in malaria vaccine design is the generation of high-quality antibody responses against the circumsporozoite protein of the malaria parasite, Plasmodium falciparum (PfCSP). To enable rational antigen design, we solved a cryo-EM structure of the highly potent anti-PfCSP antibody L9 in complex with recombinant PfCSP. We found that L9 Fab binds multivalently to the minor (NPNV) repeat domain, which is stabilized by a unique set of affinity-matured homotypic, antibody-antibody contacts. Molecular dynamics simulations revealed a critical role of the L9 light chain in integrity of the homotypic interface, which likely impacts PfCSP affinity and protective efficacy. These findings reveal the molecular mechanism of the unique NPNV selectivity of L9 and emphasize the importance of anti-homotypic affinity maturation in protective immunity against P. falciparum.

Target-agnostic identification of human antibodies toPlasmodium falciparumsexual forms reveals cross stage recognition of glutamate-rich repeats

“…A most revealing observation from our structure is the presence of affinity-matured antibody-antibody homotypic interactions in the context of recognizing repetitive tandem glutamate residues present across the Pf proteome. The finding that B1E11K targets a repetitive epitope whilst engaging in affinity-matured homotypic interactions is similar to how Abs elicited against repetitive elements of CSP can also bind through homotypic interactions (12) (14) (15) (13) (16) (19) (52) (17) (18) (11). We have previously shown that B cells expressing B cell receptors (BCRs) interacting via homotypic interactions activate more robustly in comparison to B cells that have mutated BCRs that disrupt this interaction (12).…”

“…Protective Abs elicited against CSP primarily target this immunodominant repeat region. A large proportion of these Abs engage in homotypic interactions which are characterized by direct interactions between two antibodies' variable regions when bound to adjacent repetitive epitopes (11) (12) (13) (14) (15) (16) (17) (18) (19). Such interactions have been demonstrated to augment B cell activation and contribute to shaping the humoral response to CSP (12).…”

Molecular determinants of cross-reactivity and potency by VH3-33 antibodies against the Plasmodium falciparum circumsporozoite protein

“…In fact, homotypic interactions and spiral ordering of PfCSP have been described in a monoclonal context by X-ray crystal structures with longer peptides containing two or more epitopes and cryoelectron microscopy studies with recombinant PfCSP. 22 , 23 , 27 , 29 , 30 , 55 Whether these phenomena occur in a polyclonal setting remains to be seen. In the biological context of different Pf strains, the diversity of PfCSP repeat valency and motif organization as well as possible differences in PfCSP structural propensities may have varying effects on the functionality of cross-reactive mAbs with distinct binding modes.…”

“…Extensive structural characterization of anti-PfCSP repeat mAbs has resulted in the elucidation of a wide range of PfCSP recognition modes because different inhibitory mAbs induce different binding conformations for otherwise largely disordered repeat motifs. 15 , 16 , 17 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 This diversity is further amplified by differential heavy-chain gene usage among these mAbs, including IGHV3-30 (mAb 317), 15 IGHV1-3 (mAb CIS43), 17 IGHV3-49 (mAb 4493), 21 and IGHV3-33 (mAb L9). 18 As a result of such broad diversity, although distinct antibody-bound epitope conformations have recently been linked to varying levels of potency, 27 the effects of binding mode on mAb inhibitory efficacy are still ambiguous.…”

Somatic hypermutation-mediated paratope flexibility improves the cross-reactivity of human malaria antibodies

“…Protective anti-PfCSP antibodies target the central repeat domain and the N-terminal junction (Triller et al, 2017;Oyen et al, 2017Oyen et al, , 2018Kisalu et al, 2018;Tan et al, 2018;Murugan et al, 2020;Wang et al, 2020;Kratochvil et al, 2021;Martin et al, 2023;Williams et al, 2024). These domains are characterised by a large number of repeating four amino acid (aa) asparagine-alanine-asparagine-proline (NANP) motifs in the central domain and NANP motifs interspersed with a few asparagine-valine-aspartate-proline (NVDP) motifs in the N-junction, which connects the repeat domain to the N-terminus and contains a single asparagine-prolineaspartate-proline (NPDP) motif.…”