Biology subjects

Pronker, M. F.

Publications and source records attributed to Pronker, M. F..

8 recordsLinked to original sources

bioRxiv2026

Affinity maturation of a single-domain antibody via rational mutagenesis informed by artificial intelligence

Antibodies can originate from various sources such as animal immunizations, patient material, DNA/RNA libraries and (AI-based) de novo design. Pre-made (e.g. synthetic) DNA libraries have substantial advantages over traditional immunization campaigns in terms of speed, cost, animal welfare, amount of required antigen and the possibility to select against otherwise problematic (e.g. toxic, unstable or expensive) antigens. The main downside is that selections from these non-immune libraries often result in binders with relatively low affinity due to the absence of in vivo affinity maturation. Now that in silico structure prediction tools are coming of age, the resulting models could conceivably be used to rationally design mutations, e.g. to enhance binding affinity. Here we used a synthetic single-domain antibody (sdAb) library to select new binders against interleukin-12 (IL-12). One of the selected candidates, 2F3, was predicted to bind to the p40 subunit of IL-12 in a manner that would compete with binding of the receptor protein IL-12R{beta}1. Intriguingly, this epitope is also targeted by the clinically approved antibodies Briakinumab and Ustekinumab, which are used to treat a variety of inflammation disorders. The predicted structure of the IL-12/sdAb complex was used to rationally design eleven point mutations, of which three showed to enhance the binding affinity. By combining these mutations, we could enhance the affinity by eightfold compared to the original lead clone. This shows that correctly (AI-)predicted protein structural models can be used for rational mutagenesis to enhance binding affinity to relevant drug targets.

biochemistry↗

bioRxiv2025

Structural basis for postfusion-specific binding to Respiratory Syncytial Virus F protein by the canonical antigenic site I antibody 131-2a

The Respiratory Syncytial Virus (RSV) Fusion (F) protein is a major target of antiviral antibodies following natural infection or vaccination and responsible for mediating fusion between the viral envelope and the host membrane. The fusion process is driven by a large-scale conformational change in F, switching irreversibly from the metastable prefusion state to the stable postfusion conformation. Previous research has identified six distinct antigenic sites in RSV-F, termed sites O, I, II, III, IV, and V. Of these, only antigenic site I is fully specific to the postfusion conformation of F. A monoclonal antibody 131-2a that specifically targets postfusion F has been widely used as a research tool to probe for postfusion F and to define antigenic site I in serological studies, yet its sequence and precise epitope have remained unknown. Here we use mass spectrometry-based de novo sequencing of 131-2a to reverse engineer a recombinant product and study the epitope to define antigenic site I with molecular detail, revealing the structural basis for the antibodys specificity towards postfusion RSV-F.

immunology↗

bioRxiv2024

Structural basis for recognition of the FLAG-1 tag by anti-FLAG M2

The FLAG-tag/anti-FLAG system is a widely used biochemical tool for protein detection and purification. Anti-FLAG M2 is the most popular antibody against the FLAG-tag, due to its ease of use, versatility, and availability in pure form or as bead conjugate. M2 binds N-terminal, C-terminal and internal FLAG-tags and binding is calcium-independent, but the molecular basis for the FLAG-tag specificity and recognition remains unresolved. Here we present an atomic resolution (1.17 [A]) structure of the FLAG peptide in complex with the Fab of anti-FLAG M2, revealing key binding determinants. Five of the eight FLAG peptide residues form direct interactions with paratope residues. The FLAG peptide adopts a 310 helix conformation in complex with the Fab. These structural insights allowed us to rationally introduce point mutations on both the peptide and antibody side. We tested these by surface plasmon resonance, leading us to propose a shorter yet equally binding version of the FLAG-tag for the M2 antibody.

biochemistry↗

bioRxiv2023

Reverse engineering the anti-MUC1 hybridoma antibody 139H2 by mass spectrometry-based de novo sequencing

Mucin 1 (MUC1) is a transmembrane mucin expressed at the apical surface of epithelial cells at different mucosal surfaces including breast and intestine. In the gastrointestinal tract, MUC1 has a barrier function against bacterial invasion, but can also serve as an entry receptor for pathogenic Salmonella bacteria. Moreover, MUC1 is well known for its aberrant expression and glycosylation in adenocarcinomas The MUC1 extracellular domain contains a variable number of tandem repeats (VNTR) of 20 amino acids, which are heavily O-linked glycosylated.. Monoclonal antibodies against the MUC1 VNTR can be powerful tools because of their multiplicity of binding and possible applications in the diagnosis and treatment of MUC1-expressing cancers. One such antibody is the hybridoma mouse monoclonal 139H2, which is also widely used as a research tool to study non-cancer MUC1. Here we report direct mass spectrometry-based sequencing of hybridoma-derived 139H2 IgG, which enabled reverse engineering of a recombinant 139H2. The performance of the reverse engineered 139H2 IgG and its Fab fragment were validated by comparison to the hybridoma-derived product in Western blot and immunofluorescence microscopy. The reverse engineering of 139H2 allowed us to characterize binding to the VNTR peptide epitope by surface plasmon resonance (SPR) and solve the crystal structure of the 139H2 Fab fragment in complex with the MUC1 VNTR peptide. These analyses reveal the molecular basis for 139H2 binding specificity to MUC1 and its tolerance to O-glycosylation of the VNTR. The available sequence of 139H2 will allow further development of MUC1-related diagnostics, targeting and treatment strategies.

biochemistry↗

bioRxiv2023

Sialoglycan binding triggers spike opening in a human coronavirus

Coronavirus (CoV) spikes mediate receptor binding and membrane fusion, making them prime targets for neutralising antibodies. In the cases of SARS-CoV, SARS-CoV-2, and MERS-CoV, spikes transition freely between open and closed conformations to balance host cell attachment and immune evasion. The open conformation exposes domain S1B, allowing it to bind to proteinaceous cell surface receptors. It also facilitates protein refolding during spike-mediated membrane fusion. However, with a single exception, the pre-fusion spikes of all other CoVs studied so far have been observed exclusively in the closed state. This raises the possibility of regulation, where spikes more commonly transition to open states in response to specific cues, rather than spontaneously. In our study, using cryo-EM and molecular dynamics simulations, we show that the spike protein of the common cold human coronavirus HKU1 undergoes local and long-range conformational changes upon binding a sialoglycan-based primary receptor to domain S1A. This binding triggers the transition of S1B domains to the open state via allosteric inter-domain cross-talk. Our findings paint a more elaborate picture of CoV attachment, with possibilities of dual receptor usage and priming of entry as a means of immune escape.

microbiology↗

bioRxiv2022

Glycan shield of the ebolavirus envelope glycoprotein GP

The envelope glycoprotein GP of the ebolaviruses is essential for host cell attachment and entry. It is also the primary target of the protective and neutralizing antibody response in both natural infection and vaccination. GP is heavily glycosylated with up to 17 predicted N-linked sites, numerous O-linked glycans in its disordered mucin-like domain (MLD), and three predicted C-linked mannosylation sites. Glycosylation of GP is important for host cell attachment to cell-surface lectins, as well as GP stability and fusion activity. Moreover, it has been shown to shield GP from neutralizing activity of serum antibodies. Here, we use mass spectrometry-based glycoproteomics to profile the site-specific glycosylation patterns of ebolavirus GP. We detect up to 16 unique O-linked glycosylation sites in the mucin-like domain, as well as two O-linked sites in the head and glycan cap domains of the receptor-binding GP1 subunit. Multiple O-linked glycans are observed at the S/T residues of N-linked glycosylation sequons, suggesting possible crosstalk between the two types of modifications. We also confirmed the presence of C-mannosylation at W288 in the context of trimeric GP. We find heterogenous, complex N-linked glycosylation at the majority of predicted sites as expected. By contrast, the two conserved sites N257 and N563 are enriched in unprocessed high-mannose and hybrid glycans, suggesting a role in host-cell attachment via DC-SIGN/L-SIGN. We discuss our findings in the context of antibody recognition to show how glycans contribute to and restrict neutralization epitopes. This information on how N-, O-, and C-linked glycans together build the heterogeneous glycan shield of GP can guide future immunological studies and functional interpretation of ebolavirus GP-antibody interactions.

biochemistry↗

bioRxiv2021

Mass spectrometry-based sequencing of the anti-FLAG-M2 antibody using multiple proteases and a dual fragmentation scheme

Antibody sequence information is crucial to understanding the structural basis for antigen binding and enables the use of antibodies as therapeutics and research tools. Here we demonstrate a method for direct de novo sequencing of monoclonal IgG from the purified antibody products. The method uses a panel of multiple complementary proteases to generate suitable peptides for de novo sequencing by LC-MS/MS in a bottom-up fashion. Furthermore, we apply a dual fragmentation scheme, using both stepped high-energy collision dissociation (stepped HCD) and electron transfer high-energy collision dissociation (EThcD) on all peptide precursors. The method achieves full sequence coverage of the monoclonal antibody Herceptin, with an accuracy of 99% in the variable regions. We applied the method to sequence the widely used anti-FLAG-M2 mouse monoclonal antibody, which we successfully validated by remodeling a high-resolution crystal structure of the Fab and demonstrating binding to a FLAG-tagged target protein in Western blot analysis. The method thus offers robust and reliable sequences of monoclonal antibodies.

biochemistry↗

bioRxiv2020

Cryo-EM structure of coronavirus-HKU1 haemagglutinin esterase reveals architectural changes arising from prolonged circulation in humans

The human betacoronaviruses HKU1 and OC43 (subgenus Embecovirus) arose from separate zoonotic introductions, OC43 relatively recently and HKU1 apparently much longer ago. Embecovirus particles are studded with two types of surface projections called S (for spike) and HE (for haemagglutinin-esterase), with S mediating receptor-binding and membrane fusion and HE acting as a receptor-destroying enzyme. Together, they promote dynamic virion attachment to glycan-based receptors with 9-O-acetylated sialic acid as main constituent. We recently showed that adaptation of HKU1 and OC43 to replication in the human respiratory tract involved loss-of-function mutations in the lectin domain of HE. Here we present the cryo-EM structure of the [~]80 kDa, heavily glycosylated HKU1 HE at a global resolution of 3.4 [A]. Comparison to existing HE structures reveals a drastically truncated lectin domain, incompatible with sialic acid binding, but with the structure and function of the HE esterase domain left intact. Our cryo-EM structure, in combination with mass spectrometry analysis, also describes the extent of glycosylation on the now redundant lectin domain, which forms a putative glycan shield. The findings further our insight into the evolution and host adaptation of human embecoviruses and also demonstrate the utility of cryo-EM for studying small, heavily glycosylated proteins which are intractable to X-ray crystallography.

microbiology↗