Giusti, F. | Search bioRxiv

bioRxiv2024

Structural dynamics and immunogenicity of the recombinant and outer membrane vesicle-embedded Meningococcal antigen NadA

The structure and conformation adopted by protein vaccine antigens significantly influence the exposure of their antigenic determinants. Structural knowledge of antigens in native state could drive the design of recombinant vaccines that resemble their cognate native forms, although such information is often difficult to obtain, particularly for membrane proteins. Here, we assessed the structural and functional features of the native Neisseria Adhesin A (NadA), a meningococcal trimeric outer membrane protein included as soluble recombinant antigen in the 4CMenB vaccine. We used hydrogen-deuterium exchange mass spectrometry (HDX-MS) to generate a structural model of NadA and to compare the fold and structural dynamics of the recombinant NadA as soluble vaccine form, and the native NadA in situ, as embedded in meningococcal outer membrane vesicles (OMVs), complementing the HDX data with electron microscopy imaging. While their overall structures are similar, conformational differences between the two forms were observed. Especially, OMV- embedded NadA appears more susceptible to trimer opening than its cognate soluble antigen, suggesting that NadA in its native membrane could display a larger antigenic surface. Accordingly, we show that mice immunized with OMV-embedded NadA elicited antibodies with superior bactericidal activity and capable of better preventing bacterial adhesion compared to the soluble antigen. Collectively, these data support the hypothesis that protein vaccine antigens presented in native-like environments can elicit a more potent immune response than recombinant forms.

biophysics↗

bioRxiv2023

Human monoclonal antibodies reveal subdominant gonococcal and meningococcal cross-protective antigens

Gonococcus (Gc), a bacterium resistant to most antibiotics causing more than 80 million cases of gonorrhea annually, is a WHO high priority pathogen. Recently, vaccine development prospects were boosted by reports that licensed meningococcus serogroup B (MenB) vaccines provided partial protection against Gc infection. To determine antigens responsible for cross-protection, memory B cells from 4CMenB vaccinated volunteers were single-cell sorted to identify antibodies that kill Gc in a bactericidal assay. Nine different antibodies, all deriving from the IGHV4-34 germline carrying unusually long HCDR3s, recognized the PorB protein, four recognized the lipooligosaccharide (LOS), and four unknown antigens. One of the PorB antibodies, tested in vivo, provided protection from Gc infection. The identification of PorB and LOS as key antigens of gonococcal and meningococcal immunity provides a mechanistic explanation of the cross-protection observed in the clinic and shows that isolating human monoclonal antibodies from vaccinees can be instrumental for bacterial antigen discovery.

immunology↗

bioRxiv2017

The radiation of alopiine clausiliids in the Sicilian Channel (Central Mediterranean): phylogeny, patterns of morphological diversification and implications for taxonomy and conservation of Muticaria and Lampedusa

The phylogeny, biogeography and taxonomy of the alopiine clausiliids of the Sicilian Channel, belonging to the genera Lampedusa and Muticaria, were investigated using morphological (shell characters and anatomy of the reproductive system) and genetic (sequencing of a fragment of the mitochondrial large ribosomal subunit 16S rRNA, and the nuclear internal transcriber spacer 1, ITS-1 rRNA) data. Classically, the genus Lampedusa includes three species: L. imitatrix and L. melitensis occurring in circumscribed localities in western Malta and on the islet of Filfla, and L. lopadusae on Lampedusa and Lampione. The genus Muticaria includes two species in southeastern Sicily (M. siracusana and M. neuteboomi) and one in the Maltese islands (M. macrostoma), which is usually subdivided into four entities based on shell characters (macrostoma on Gozo, Comino, Cominotto and central-eastern Malta; mamotica in southeastern Gozo; oscitans on Gozo and central-western Malta; scalaris in northwestern Malta). These have sometimes been considered as subspecies and sometimes as mere morphs.\n\nThe Lampedusa of Lampedusa and Lampione form a well distinct clade from those of the Maltese Islands. The population of Lampione islet is a genetically distinct geographic form that deserves formal taxonomic recognition (as L. nodulosa or L. l. nodulosa). The Lampedusa of Malta are morphologically distinct evolutionary lineages with high levels of genetic divergence and are confirmed as distinct species (L. imitatrix and L. melitensis).\n\nThe Muticaria constitute a clearly different monophyletic clade divided into three geographical lineages corresponding to the Sicilian, Maltese and Gozitan populations. The Sicilian Muticaria form two morphologically and genetically distinguishable subclades that may either be considered subspecies of a polytypic species, or two distinct species. The relationships of Maltese and Gozitan Muticaria are complex. Two of the three Maltese morphotypes resulted monophyletic (oscitans and scalaris) while the other was separated in two lineages (macrostoma); however this picture may be biased as only few samples of macrostoma were available to study. The Gozitan morphotypes (macrostoma, mamotica and oscitans) where resolved as polyphyletic but with clear molecular evidence of mixing in some cases, indicating possible relatively recent differentiation of the Gozitan Muticaria or repetitive secondary contacts between different morphotypes. Definitive taxonomic conclusions from these results are premature. Maltese Muticaria could be subdivided into three taxa according to morphological and molecular data (M. macrostoma or M. m. macrostoma, M. oscitans or M. m. oscitans and M. scalaris or M. m scalaris). Gozitan Muticaria could be considered a distinct polytypic species (for which the oldest available name is Muticaria mamotica) subdivided into subspecies showing a morphological range from macrostoma-like to mamotica-like and oscitans like.\n\nOnly the two Maltese species of Lampedusa are legally protected (by the European Unions Habitats Directive and Maltese national legislation). The present study has shown that the alopiine clausiliids of the Sicilian Channel constitute a number of genetically and/or morphologically distinct populations that represent important pools of genetic diversity, with, in some cases, a very circumscribed distribution. As such, these populations deserve legal protection and management. It is argued that without formal taxonomic designation, it would be difficult to extend international legal protection to some of the more threatened of these populations.

zoology↗