Matthieu Masureel

C-X-C motif chemokine receptor 3 (CXCR3) is essential for immune cell functions and pivotal in T helper 1 cell infiltration in autoimmune and chronic inflammatory diseases and in tumor proliferation and metastasis, but the mechanisms by which the endogenous ligands CXCL9, CXCL10, and CXCL11 differentially recognize and activate CXCR3 are not fully understood. Here, we present cryo–electron microscopy structures of all three chemokine-CXCR3-G _i complexes, complemented by cell binding studies and functional mutagenesis data. We systematically compare the pharmacological and interaction profiles of CXCL9, CXCL10, and CXCL11 to rationalize their varying efficacies and potencies and to reveal the critical role of the membrane-distal CXCR3 N terminus in ligand binding and signaling. Using chimeric chemokines and molecular dynamics, we reveal the signaling plasticity of chemokine ligands and signaling determinants. Together, these insights enable us to propose a multimodal binding and activation framework that explains CXCR3 chemokine ligand multispecificity and signaling versatility and offer tools to interrogate and modulate CXCR3 biology.

Background/Objectives: Nature has evolved millions of venom-derived peptides with diverse biological functions, a substantial fraction of which target complex membrane proteins such as G-protein-coupled receptors and ion channels. Many of these peptides are stabilized by multiple disulfide bonds, endowing them with exceptional structural stability and favorable pharmacological properties. Methods: Leveraging this natural diversity, we developed a robust venom peptide therapeutics discovery system built on phage display technology and constructed a library using approximately 482 venom-derived scaffolds. The library design was guided by a machine learning (ML) model capable of predicting mutation-tolerant residues that preserve peptide foldability, maximizing structural integrity and sequence diversity. Results: The resulting VCX library was evaluated through screening against four diverse targets (CD47, DLL3, IL33, and P2X7R), yielding strong binders for all four, a success rate of 100%. Furthermore, by integrating high-throughput recombinant expression of thioredoxin–venom fusion proteins along with ML-assisted affinity maturation, we rapidly identified potential leads for DLL3 binders. Conclusions: This venom-based discovery platform offers significant advantages in both functionality and developability compared with conventional peptide discovery approaches. By combining natural structural diversity, ML-guided design, and recombinant expression, it enables efficient identification of “antibody-like” binders with molecular weights much smaller than those of antibodies. Consequently, it provides a powerful strategy for developing next-generation peptide therapeutics targeting challenging protein–protein interactions and complex membrane proteins.

Background: The pro-inflammatory cytokine, interleukin-18 (IL-18), plays an instrumental role in bolstering anti-tumor immunity. However, the therapeutic application of IL-18 has been limited due to its susceptibility to neutralization by IL-18 binding protein (IL-18BP), short in vivo half-life, and unfavorable physicochemical properties. Methods: In order to overcome the poor drug-like properties of IL-18, we installed an artificial disulfide bond, removed the native, unpaired cysteines, and fused the stabilized cytokine to an IgG Fc domain. The stability, potency, pharmacokinetic and pharmacodynamic properties as well as efficacy of disulfide-stabilized IL-18 Fc-fusion (dsIL-18-Fc) were assessed via in vitro and in vivo studies. Results: The stability and mammalian host cell production yields of dsIL-18-Fc were improved, compared to the wild-type (WT) cytokine, while maintaining its biological potency and interactions with IL-18 receptor α (IL-18Rα) and IL-18BP. Recombinant fusion of the cytokine to an IgG Fc domain provided extended half-life. Notably, despite maintaining sensitivity to IL-18BP, dsIL-18-Fc was effective at activating both T and natural killer (NK) cells, and elicited a strong anti-tumor response, either as a single agent, or in conjunction with anti-programmed cell death-ligand 1 (anti-PD-L1) therapy. Conclusions: We engineered IL-18 for reinforced stability, extended half-life, and improved manufacturability. The therapeutic benefit of dsIL-18-Fc, coupled with a more favorable manufacturability profile and enhanced drug-like properties, underscores the potential utility of this engineered cytokine in cancer immunotherapy.

The heterogeneity inherent in today’s biotherapeutics, especially as a result of heavy glycosylation, can affect a molecule’s safety and efficacy. Characterizing this heterogeneity is crucial for drug development and quality assessment, but existing methods are limited in their ability to analyze intact glycoproteins or other heterogeneous biotherapeutics. Here, we present an approach to the molecular assessment of biotherapeutics that uses proton-transfer charge-reduction with gas-phase fractionation to analyze intact heterogeneous and/or glycosylated proteins by mass spectrometry. The method provides a detailed landscape of the intact molecular weights present in biotherapeutic protein preparations in a single experiment. For glycoproteins in particular, the method may offer insights into glycan composition when coupled with a suitable bioinformatic strategy. We tested the approach on various biotherapeutic molecules, including Fc-fusion, VHH-fusion, and peptide-bound MHC class II complexes to demonstrate efficacy in measuring the proteoform-level diversity of biotherapeutics. Notably, we inferred the glycoform distribution for hundreds of molecular weights for the eight-times glycosylated fusion drug IL22-Fc, enabling correlations between glycoform sub-populations and the drug’s pharmacological properties. Our method is broadly applicable and provides a powerful tool to assess the molecular heterogeneity of emerging biotherapeutics.

Rabbits produce robust antibody responses and have unique features in their antibody repertoire that make them an attractive alternative to rodents for in vivo discovery. However, the frequent occurrence of a non-canonical disulfide bond between complementarity-determining region (CDR) H1 (C35a) and CDRH2 (C50) is often seen as a liability for therapeutic antibody development, despite limited reports of its effect on antibody binding, function, and stability. Here, we describe the discovery and humanization of a human-mouse cross-reactive anti-programmed cell death 1 (PD-1) monoclonal rabbit antibody, termed h1340.CC, which possesses this non-canonical disulfide bond. Initial removal of the non-canonical disulfide resulted in a loss of PD-1 affinity and cross-reactivity, which led us to explore protein engineering approaches to recover these. First, guided by the sequence of a related clone and the crystal structure of h1340.CC in complex with PD-1, we generated variant h1340.SA.LV with a potency and cross-reactivity similar to h1340.CC, but only partially recovered affinity. Side-by-side developability assessment of both h1340.CC and h1340.SA.LV indicate that they possess similar, favorable properties. Next, and prompted by recent developments in machine learning (ML)-guided protein engineering, we used an unbiased ML- and structure-guided approach to rapidly and efficiently generate a different variant with recovered affinity. Our case study thus indicates that, while the non-canonical inter-CDR disulfide bond found in rabbit antibodies does not necessarily constitute an obstacle to therapeutic antibody development, combining structure- and ML-guided approaches can provide a fast and efficient way to improve antibody properties and remove potential liabilities.

The C-C motif chemokine receptor 8 (CCR8) is a class A G-protein coupled receptor that has emerged as a promising therapeutic target in cancer. Targeting CCR8 with an antibody has appeared to be an attractive therapeutic approach, but the molecular basis for chemokine-mediated activation and antibody-mediated inhibition of CCR8 are not fully elucidated. Here, we obtain an antagonist antibody against human CCR8 and determine structures of CCR8 in complex with either the antibody or the endogenous agonist ligand CCL1. Our studies reveal characteristic antibody features allowing recognition of the CCR8 extracellular loops and CCL1-CCR8 interaction modes that are distinct from other chemokine receptor - ligand pairs. Informed by these structural insights, we demonstrate that CCL1 follows a two-step, two-site binding sequence to CCR8 and that antibody-mediated inhibition of CCL1 signaling can occur by preventing the second binding event. Together, our results provide a detailed structural and mechanistic framework of CCR8 activation and inhibition that expands our molecular understanding of chemokine - receptor interactions and offers insight into the development of therapeutic antibodies targeting chemokine GPCRs.

NOX2 is the prototypical member of the NADPH oxidase NOX superfamily and produces superoxide (O₂^•−), a key reactive oxygen species (ROS) that is essential in innate and adaptive immunity. Mutations that lead to deficiency in NOX2 activity correlate with increased susceptibility to bacterial and fungal infections, resulting in chronic granulomatous disease. The core of NOX2 is formed by a heterodimeric transmembrane complex composed of NOX2 (formerly gp91) and p22, but a detailed description of its structural architecture is lacking. Here, we present the structure of the human NOX2 core complex bound to a selective anti-NOX2 antibody fragment. The core complex reveals an intricate extracellular topology of NOX2, a four-transmembrane fold of the p22 subunit, and an extensive transmembrane interface which provides insights into NOX2 assembly and activation. Functional assays uncover an inhibitory activity of the 7G5 antibody mediated by internalization-dependent and internalization-independent mechanisms. Overall, our results provide insights into the NOX2 core complex architecture, disease-causing mutations, and potential avenues for selective NOX2 pharmacological modulation.

Significance: The molecular origin of basal activity in G protein coupled receptors and its suppression by inverse agonists are poorly understood. Here we employ pressure-resolved DEER spectroscopy to explore the structural origin of basal activity and the mechanism of inverse agonism in the β ₂ adrenergic receptor. Collectively, the results support a conformational selection model wherein basal activity is due to a preexisting equilibrium between inactive and active conformations in the unliganded receptor, and inverse agonists stabilize the inactive conformation. Furthermore, the results illustrate the importance of rare states in molecular mechanisms of protein function and the capability of pressure-resolved DEER for revealing structural features of sparsely populated conformations of membrane proteins and for determining their thermodynamic properties.

The β₂ adrenergic receptor (β₂AR) signals through both G_s and G_i in cardiac myocytes, and the G_i pathway counteracts the G_s pathway. However, G_i coupling is much less efficient than G_s coupling in most cell-based and biochemical assays, making it difficult to study β₂AR−G_i interactions. Here we investigate the role of phospholipid composition on G_s and G_i coupling. While negatively charged phospholipids are known to enhance agonist affinity and stabilize an active state of the β₂AR, we find that they impair coupling to G_i3 and facilitate coupling to G_s. Positively charged Ca²⁺ and Mg²⁺, known to interact with the negative charge on phospholipids, facilitates G_i3 coupling. Mutational analysis suggests that Ca²⁺ coordinates an interaction between phospholipid and the negatively charged EDGE motif on the amino terminal helix of G_i3. Taken together, our observations suggest that local membrane charge modulates the interaction between β₂AR and competing G protein subtypes.

In the version of this paper originally published, the structure for epinephrine shown in Figure 1a was redrawn with an extra carbon. The structure has been replaced in the HTML and PDF versions of the article. The original and corrected versions of the structure are shown below.