Insights from structure-activity relationships and the binding mode of peptidic α-ketoamide inhibitors of the malaria drug target subtilisin-like SUB1.

Plasmodium multi-resistance, including against artemisinin, seriously threatens malaria treatment and control. Hence, new drugs are urgently needed, ideally targeting different parasitic stages, which are not yet targeted by current drugs. The SUB1 protease is involved in both hepatic and blood stages due to its essential role in the egress of parasites from host cells, and, as potential new target, it would meet the above criteria. We report here the synthesis as well as the biological and structural evaluation of substrate-based α-ketoamide SUB1 pseudopeptidic inhibitors encompassing positions P4-P2'. By individually substituting each position of the reference compound 1 (MAM-117, Ac-Ile-Thr-Ala-AlaCO-Asp-Glu (Oall)-NH2), we better characterized the structural determinants for SUB1 binding. We first identified compound 8 with IC50 values of 50 and 570 nM against Pv- and PfSUB1, respectively (about 3.5-fold higher potency compared to 1). Compound 8 inhibited P. falciparum merozoite egress in culture by 37% at 100 µM. By increasing the overall hydrophobicity of the compounds, we could improve the PfSUB1 inhibition level and antiparasitic activity, as shown with compound 40 (IC50 values of 12 and 10 nM against Pv- and PfSUB1, respectively, IC50 value of 23 µM on P. falciparum merozoite egress). We also found that 8 was highly selective towards SUB1 over three mammalian serine peptidases, supporting the promising value of this compound. Finally, several crystal 3D-structures of SUB1-inhibitor complexes, including with 8, were solved at high resolution to decipher the binding mode of these compounds.

Prodomain-driven enzyme dimerization: a pH-dependent autoinhibition mechanism that controls Plasmodium Sub1 activity before merozoite egress.

Malaria symptoms are associated with the asexual multiplication of Plasmodium falciparum within human red blood cells (RBCs) and fever peaks coincide with the egress of daughter merozoites following the rupture of the parasitophorous vacuole (PV) and the RBC membranes. Over the last two decades, it has emerged that the release of competent merozoites is tightly regulated by a complex cascade of events, including the unusual multi-step activation mechanism of the pivotal subtilisin-like protease 1 (Sub1) that takes place in three different cellular compartments and remains poorly understood. Following an initial auto-maturation in the endoplasmic reticulum (ER) between its pro- and catalytic domains, the Sub1 prodomain (PD) undergoes further cleavages by the parasite aspartic protease plasmepsin X (PmX) within acidic secretory organelles that ultimately lead to full Sub1 activation upon discharge into the PV. Here, we report the crystal structure of full-length P. falciparum Sub1 (PfS1FL) and demonstrate, through structural, biochemical, and biophysical studies, that the atypical Plasmodium-specific Sub1 PD directly promotes the assembly of inactive enzyme homodimers at acidic pH, whereas Sub1 is primarily monomeric at neutral pH. Our results shed new light into the finely tuned Sub1 spatiotemporal activation during secretion, explaining how PmX processing and full activation of Sub1 can occur in different cellular compartments, and uncover a robust mechanism of pH-dependent subtilisin autoinhibition that plays a key role in P. falciparum merozoites egress from infected host cells.IMPORTANCEMalaria fever spikes are due to the rupture of infected erythrocytes, allowing the egress of Plasmodium sp. merozoites and further parasite propagation. This fleeting tightly regulated event involves a cascade of enzymes, culminating with the complex activation of the subtilisin-like protease 1, Sub1. Differently than other subtilisins, Sub1 activation strictly depends upon the processing by a parasite aspartic protease within acidic merozoite secretory organelles. However, Sub1 biological activity is required in the pH neutral parasitophorous vacuole, to prime effectors involved in the rupture of the vacuole and erythrocytic membranes. Here, we show that the unusual, parasite-specific Sub1 prodomain is directly responsible for its acidic-dependent dimerization and autoinhibition, required for protein secretion, before its full activation at neutral pH in a monomeric form. pH-dependent Sub1 dimerization defines a novel, essential regulatory element involved in the finely tuned spatiotemporal activation of the egress of competent Plasmodium merozoites.

Structural and enzymatic evidence for the methylation of the ACK1 tyrosine kinase by the histone lysine methyltransferase SETD2.

SETD2 (SET-domain containing protein 2) is a histone methyltransferase (HMT) of the SET family responsible for the trimethylation of K36 of histone H3, thus producing the epigenetic mark H3K36me3. Recent studies have shown that certain SET family HMTs, such as SMYD2, SMYD3 or SETDB1 can also methylate protein kinases and therefore be involved in signaling pathways. Here we provide structural and enzymatic evidence showing that SETD2 methylates the protein tyrosine kinase ACK1 in vitro. ACK1 is recognized as a major integrator of signaling from various receptor tyrosine kinases. Using ACK1 peptides and recombinant proteins, we show that SETD2 methylates the K514 residue of ACK1 generating K514 mono, di or tri-methylation. Interestingly, K514 is found in a "H3K36-like" motif of ACK1 which is known to be post-translationally modified and to be involved in protein-protein interaction. The crystal structure of SETD2 catalytic domain in complex with an ACK1 peptide further provides the structural basis for the methylation of ACK1 K514 by SETD2. Our work therefore strongly suggests that ACK1 could be a novel non-histone substrate of SETD2 and further supports that SET HMTs, such as SETD2, could be involved in both epigenetic regulations and cell signaling.

Eukaryotic-like gephyrin and cognate membrane receptor coordinate corynebacterial cell division and polar elongation.

The order Corynebacteriales includes major industrial and pathogenic Actinobacteria such as Corynebacterium glutamicum or Mycobacterium tuberculosis. These bacteria have multi-layered cell walls composed of the mycolyl-arabinogalactan-peptidoglycan complex and a polar growth mode, thus requiring tight coordination between the septal divisome, organized around the tubulin-like protein FtsZ, and the polar elongasome, assembled around the coiled-coil protein Wag31. Here, using C. glutamicum, we report the discovery of two divisome members: a gephyrin-like repurposed molybdotransferase (Glp) and its membrane receptor (GlpR). Our results show how cell cycle progression requires interplay between Glp/GlpR, FtsZ and Wag31, showcasing a crucial crosstalk between the divisome and elongasome machineries that might be targeted for anti-mycobacterial drug discovery. Further, our work reveals that Corynebacteriales have evolved a protein scaffold to control cell division and morphogenesis, similar to the gephyrin/GlyR system that mediates synaptic signalling in higher eukaryotes through network organization of membrane receptors and the microtubule cytoskeleton.

3D structures of the Plasmodium vivax subtilisin-like drug target SUB1 reveal conformational changes to accommodate a substrate-derived α-ketoamide inhibitor.

The constant selection and propagation of multi-resistant Plasmodium sp. parasites require the identification of new antimalarial candidates involved in as-yet untargeted metabolic pathways. Subtilisin-like protease 1 (SUB1) belongs to a new generation of drug targets because it plays a crucial role during egress of the parasite from infected host cells at different stages of its life cycle. SUB1 is characterized by an unusual pro-region that tightly interacts with its cognate catalytic domain, thus precluding 3D structural analysis of enzyme-inhibitor complexes. In the present study, to overcome this limitation, stringent ionic conditions and controlled proteolysis of recombinant full-length P. vivax SUB1 were used to obtain crystals of an active and stable catalytic domain (PvS1Cat) without a pro-region. High-resolution 3D structures of PvS1Cat, alone and in complex with an α-ketoamide substrate-derived inhibitor (MAM-117), showed that, as expected, the catalytic serine of SUB1 formed a covalent bond with the α-keto group of the inhibitor. A network of hydrogen bonds and hydrophobic interactions stabilized the complex, including at the P1' and P2' positions of the inhibitor, although P' residues are usually less important in defining the substrate specificity of subtilisins. Moreover, when associated with a substrate-derived peptidomimetic inhibitor, the catalytic groove of SUB1 underwent significant structural changes, particularly in its S4 pocket. These findings pave the way for future strategies for the design of optimized SUB1-specific inhibitors that may define a novel class of antimalarial candidates.

Insight into the role of the Bateman domain at the molecular and physiological levels through engineered IMP dehydrogenases.

Inosine 5'-monophosphate (IMP) dehydrogenase (IMPDH) is an ubiquitous enzyme that catalyzes the NAD+ -dependent oxidation of inosine 5'-monophosphate into xanthosine 5'-monophosphate. This enzyme is formed of two distinct domains, a core domain where the catalytic reaction occurs, and a less-conserved Bateman domain. Our previous studies gave rise to the classification of bacterial IMPDHs into two classes, according to their oligomeric and kinetic properties. MgATP is a common effector but cause to different effects when it binds within the Bateman domain: it is either an allosteric activator for Class I IMPDHs or a modulator of the oligomeric state for Class II IMPDHs. To get insight into the role of the Bateman domain in the dissimilar properties of the two classes, deleted variants of the Bateman domain and chimeras issued from the interchange of the Bateman domain between the three selected IMPDHs have been generated and characterized using an integrative structural biology approach. Biochemical, biophysical, structural, and physiological studies of these variants unveil the Bateman domain as being the carrier of the molecular behaviors of both classes.

Interactions of the protein tyrosine phosphatase PTPN3 with viral and cellular partners through its PDZ domain: insights into structural determinants and phosphatase activity.

The human protein tyrosine phosphatase non-receptor type 3 (PTPN3) is a phosphatase containing a PDZ (PSD-95/Dlg/ZO-1) domain that has been found to play both tumor-suppressive and tumor-promoting roles in various cancers, despite limited knowledge of its cellular partners and signaling functions. Notably, the high-risk genital human papillomavirus (HPV) types 16 and 18 and the hepatitis B virus (HBV) target the PDZ domain of PTPN3 through PDZ-binding motifs (PBMs) in their E6 and HBc proteins respectively. This study focuses on the interactions between the PTPN3 PDZ domain (PTPN3-PDZ) and PBMs of viral and cellular protein partners. We solved the X-ray structures of complexes between PTPN3-PDZ and PBMs of E6 of HPV18 and the tumor necrosis factor-alpha converting enzyme (TACE). We provide new insights into key structural determinants of PBM recognition by PTPN3 by screening the selectivity of PTPN3-PDZ recognition of PBMs, and by comparing the PDZome binding profiles of PTPN3-recognized PBMs and the interactome of PTPN3-PDZ. The PDZ domain of PTPN3 was known to auto-inhibit the protein's phosphatase activity. We discovered that the linker connecting the PDZ and phosphatase domains is involved in this inhibition, and that the binding of PBMs does not impact this catalytic regulation. Overall, the study sheds light on the interactions and structural determinants of PTPN3 with its cellular and viral partners, as well as on the inhibitory role of its PDZ domain on its phosphatase activity.

DNA-binding mechanism and evolution of replication protein A.

Replication Protein A (RPA) is a heterotrimeric single stranded DNA-binding protein with essential roles in DNA replication, recombination and repair. Little is known about the structure of RPA in Archaea, the third domain of life. By using an integrative structural, biochemical and biophysical approach, we extensively characterize RPA from Pyrococcus abyssi in the presence and absence of DNA. The obtained X-ray and cryo-EM structures reveal that the trimerization core and interactions promoting RPA clustering on ssDNA are shared between archaea and eukaryotes. However, we also identified a helical domain named AROD (Acidic Rpa1 OB-binding Domain), and showed that, in Archaea, RPA forms an unanticipated tetrameric supercomplex in the absence of DNA. The four RPA molecules clustered within the tetramer could efficiently coat and protect stretches of ssDNA created by the advancing replisome. Finally, our results provide insights into the evolution of this primordial replication factor in eukaryotes.

The crystal structure of a simian Foamy Virus receptor binding domain provides clues about entry into host cells.

The surface envelope glycoprotein (Env) of all retroviruses mediates virus binding to cells and fusion of the viral and cellular membranes. A structure-function relationship for the HIV Env that belongs to the Orthoretrovirus subfamily has been well established. Structural information is however largely missing for the Env of Foamy viruses (FVs), the second retroviral subfamily. In this work we present the X-ray structure of the receptor binding domain (RBD) of a simian FV Env at 2.57 Å resolution, revealing two subdomains and an unprecedented fold. We have generated a model for the organization of the RBDs within the trimeric Env, which indicates that the upper subdomains form a cage-like structure at the apex of the Env, and identified residues K342, R343, R359 and R369 in the lower subdomain as key players for the interaction of the RBD and viral particles with heparan sulfate.

The MksG nuclease is the executing part of the bacterial plasmid defense system MksBEFG.

Cells are continuously facing the risk of taking up foreign DNA that can compromise genomic integrity. Therefore, bacteria are in a constant arms race with mobile genetic elements such as phages, transposons and plasmids. They have developed several active strategies against invading DNA molecules that can be seen as a bacterial 'innate immune system'. Here, we investigated the molecular arrangement of the Corynebacterium glutamicum MksBEFG complex, which is homologous to the MukBEF condensin system. We show here that MksG is a nuclease that degrades plasmid DNA. The crystal structure of MksG revealed a dimeric assembly through its C-terminal domain that is homologous to the TOPRIM domain of the topoisomerase II family of enzymes and contains the corresponding ion binding site essential for DNA cleavage in topoisomerases. The MksBEF subunits exhibit an ATPase cycle in vitro and we reason that this reaction cycle, in combination with the nuclease activity provided by MksG, allows for processive degradation of invading plasmids. Super-resolution localization microscopy revealed that the Mks system is spatially regulated via the polar scaffold protein DivIVA. Introduction of plasmids results in an increase in DNA bound MksG, indicating an activation of the system in vivo.

Structure, function, and evolution of the Orthobunyavirus membrane fusion glycoprotein.

La Crosse virus, responsible for pediatric encephalitis in the United States, and Schmallenberg virus, a highly teratogenic veterinary virus in Europe, belong to the large Orthobunyavirus genus of zoonotic arthropod-borne pathogens distributed worldwide. Viruses in this under-studied genus cause CNS infections or fever with debilitating arthralgia/myalgia syndromes, with no effective treatment. The main surface antigen, glycoprotein Gc (∼1,000 residues), has a variable N-terminal half (GcS) targeted by the patients' antibody response and a conserved C-terminal moiety (GcF) responsible for membrane fusion during cell entry. Here, we report the X-ray structure of post-fusion La Crosse and Schmallenberg virus GcF, revealing the molecular determinants for hairpin formation and trimerization required to drive membrane fusion. We further experimentally confirm the role of residues in the fusion loops and in a vestigial endoplasmic reticulum (ER) translocation sequence at the GcS-GcF junction. The resulting knowledge provides essential molecular underpinnings for future development of potential therapeutic treatments and vaccines.

Trypanosoma brucei RRP44: a versatile enzyme for processing structured and non-structured RNA substrates.

Rrp44/Dis3 is a conserved eukaryotic ribonuclease that acts on processing and degradation of nearly all types of RNA. It contains an endo- (PIN) and an exonucleolytic (RNB) domain and, its depletion in model organisms supports its essential function for cell viability. In Trypanosoma brucei, depletion of Rrp44 (TbRRP44) blocks maturation of ribosomal RNA, leading to disruption of ribosome synthesis and inhibition of cell proliferation. We have determined the crystal structure of the exoribonucleolytic module of TbRRP44 in an active conformation, revealing novel details of the catalytic mechanism of the RNB domain. For the first time, the position of the second magnesium involved in the two-metal-ion mechanism was determined for a member of the RNase II family. In vitro, TbRRP44 acts preferentially on non-structured uridine-rich RNA substrates. However, we demonstrated for the first time that both TbRRP44 and its homologue from Saccharomyces cerevisiae can also degrade structured substrates without 3'-end overhang, suggesting that Rrp44/Dis3 ribonucleases may be involved in degradation of a wider panel of RNA than has been assumed. Interestingly, deletion of TbRRP44 PIN domain impairs RNA binding to different extents, depending on the type of substrate.

Structure and dynamic association of an assembly platform subcomplex of the bacterial type II secretion system.

Type II secretion systems (T2SSs) allow diderm bacteria to secrete hydrolytic enzymes, adhesins, or toxins important for growth and virulence. To promote secretion of folded proteins, T2SSs assemble periplasmic filaments called pseudopili or endopili at an inner membrane subcomplex, the assembly platform (AP). Here, we combined biophysical approaches, nuclear magnetic resonance (NMR) and X-ray crystallography, to study the Klebsiella AP components PulL and PulM. We determined the structure and associations of their periplasmic domains and describe the structure of the heterodimer formed by their ferredoxin-like domains. We show how structural complementarity and plasticity favor their association during the secretion process. Cysteine scanning and crosslinking data provided additional constraints to build a structural model of the PulL-PulM assembly in the cellular context. Our structural and functional insights, together with the relative cellular abundance of its components, support the role of AP as a dynamic hub that orchestrates pilus polymerization.

FtsEX-independent control of RipA-mediated cell separation in Corynebacteriales.

The bacterial cell wall is a multi-layered mesh, whose major component is peptidoglycan (PG), a sugar polymer cross-linked by short peptide stems. During cell division, a careful balance of PG synthesis and degradation, precisely coordinated both in time and space, is necessary to prevent uncontrolled destruction of the cell wall. In Corynebacteriales, the D,L endopeptidase RipA has emerged as a major PG hydrolase for cell separation, and RipA defaults have major implications for virulence of the human pathogens Mycobacterium tuberculosis and Corynebacterium diphtheriae. However, the precise mechanisms by which RipA mediates cell separation remain elusive. Here we report phylogenetic, biochemical, and structural analysis of the Corynebacterium glutamicum homologue of RipA, Cg1735. The crystal structures of full-length Cg1735 in two different crystal forms revealed the C-terminal NlpC/P60 catalytic domain obtruded by its N-terminal conserved coiled-coil domain, which locks the enzyme in an autoinhibited state. We show that this autoinhibition is relieved by the extracellular core domain of the transmembrane septal protein Cg1604. The crystal structure of Cg1604 revealed a (ß/α) protein with an overall topology similar to that of receiver domains from response regulator proteins. The atomic model of the Cg1735-Cg1604 complex, based on bioinformatical and mutational analysis, indicates that a conserved, distal-membrane helical insertion in Cg1604 is responsible for Cg1735 activation. The reported data provide important insights into how intracellular cell division signal(s), yet to be identified, control PG hydrolysis during RipA-mediated cell separation in Corynebacteriales.

Dynamics and structural changes of calmodulin upon interaction with the antagonist calmidazolium.

BACKGROUND: Calmodulin (CaM) is an evolutionarily conserved eukaryotic multifunctional protein that functions as the major sensor of intracellular calcium signaling. Its calcium-modulated function regulates the activity of numerous effector proteins involved in a variety of physiological processes in diverse organs, from proliferation and apoptosis, to memory and immune responses. Due to the pleiotropic roles of CaM in normal and pathological cell functions, CaM antagonists are needed for fundamental studies as well as for potential therapeutic applications. Calmidazolium (CDZ) is a potent small molecule antagonist of CaM and one the most widely used inhibitors of CaM in cell biology. Yet, CDZ, as all other CaM antagonists described thus far, also affects additional cellular targets and its lack of selectivity hinders its application for dissecting calcium/CaM signaling. A better understanding of CaM:CDZ interaction is key to design analogs with improved selectivity. Here, we report a molecular characterization of CaM:CDZ complexes using an integrative structural biology approach combining SEC-SAXS, X-ray crystallography, HDX-MS, and NMR. RESULTS: We provide evidence that binding of a single molecule of CDZ induces an open-to-closed conformational reorientation of the two domains of CaM and results in a strong stabilization of its structural elements associated with a reduction of protein dynamics over a large time range. These CDZ-triggered CaM changes mimic those induced by CaM-binding peptides derived from physiological protein targets, despite their distinct chemical natures. CaM residues in close contact with CDZ and involved in the stabilization of the CaM:CDZ complex have been identified. CONCLUSION: Our results provide molecular insights into CDZ-induced dynamics and structural changes of CaM leading to its inhibition and open the way to the rational design of more selective CaM antagonists. Calmidazolium is a potent and widely used inhibitor of calmodulin, a major mediator of calcium-signaling in eukaryotic cells. Structural characterization of calmidazolium-binding to calmodulin reveals that it triggers open-to-closed conformational changes similar to those induced by calmodulin-binding peptides derived from enzyme targets. These results provide molecular insights into CDZ-induced dynamics and structural changes of CaM leading to its inhibition and open the way to the rational design of more selective CaM antagonists.

Interactions of Severe Acute Respiratory Syndrome Coronavirus 2 Protein E With Cell Junctions and Polarity PSD-95/Dlg/ZO-1-Containing Proteins.

The C-terminus of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) protein E contains a PBM (PDZ-binding motif) targeting PDZ (PSD-95/Dlg/ZO-1) domains, which is identical to the PBM of SARS-CoV. The latter is involved in the pathogenicity of the virus. Recently, we identified 10 human PDZ-containing proteins showing significant interactions with SARS-CoV-2 protein E PBM. We selected several of them involved in cellular junctions and cell polarity (TJP1, PARD3, MLLT4, and LNX2) and MPP5/PALS1 previously shown to interact with SARS-CoV E PBM. Targeting cellular junctions and polarity components is a common strategy by viruses to hijack cell machinery to their advantage. In this study, we showed that these host PDZ domains TJP1, PARD3, MLLT4, LNX2, and MPP5/PALS1 interact in a PBM-dependent manner in vitro and colocalize with the full-length E protein in cellulo, sequestrating the PDZ domains to the Golgi compartment. We solved three crystal structures of complexes between human LNX2, MLLT4, and MPP5 PDZs and SARS-CoV-2 E PBM highlighting its binding preferences for several cellular targets. Finally, we showed different affinities for the PDZ domains with the original SARS-CoV-2 C-terminal sequence containing the PBM and the one of the beta variant that contains a mutation close to the PBM. The acquired mutations in the E protein localized near the PBM might have important effects both on the structure and the ion-channel activity of the E protein and on the host machinery targeted by the variants during the infection.

Structural basis for the allosteric inhibition of UMP kinase from Gram-positive bacteria, a promising antibacterial target.

Tuberculosis claims significantly more than one million lives each year. A feasible way to face the issue of drug resistance is the development of new antibiotics. Bacterial uridine 5'-monophosphate (UMP) kinase is a promising target for novel antibiotic discovery as it is essential for bacterial survival and has no counterpart in human cells. The UMP kinase from M. tuberculosis is also a model of particular interest for allosteric regulation with two effectors, GTP (positive) and UTP (negative). In this study, using X-ray crystallography and cryo-electron microscopy, we report for the first time a detailed description of the negative effector UTP-binding site of a typical Gram-positive behaving UMP kinase. Comparison between this snapshot of low affinity for Mg-ATP with our previous 3D-structure of the GTP-bound complex of high affinity for Mg-ATP led to a better understanding of the cooperative mechanism and the allosteric regulation of UMP kinase. Thermal shift assay and circular dichroism experiments corroborate our model of an inhibition by UTP linked to higher flexibility of the Mg-ATP-binding domain. These new structural insights provide valuable knowledge for future drug discovery strategies targeting bacterial UMP kinases.

Structural basis of synergistic neutralization of Crimean-Congo hemorrhagic fever virus by human antibodies.

Crimean-Congo hemorrhagic fever virus (CCHFV) is the most widespread tick-borne zoonotic virus, with a 30% case fatality rate in humans. Structural information is lacking in regard to the CCHFV membrane fusion glycoprotein Gc­the main target of the host neutralizing antibody response­as well as antibody­mediated neutralization mechanisms. We describe the structure of prefusion Gc bound to the antigen-binding fragments (Fabs) of two neutralizing antibodies that display synergy when combined, as well as the structure of trimeric, postfusion Gc. The structures show the two Fabs acting in concert to block membrane fusion, with one targeting the fusion loops and the other blocking Gc trimer formation. The structures also revealed the neutralization mechanism of previously reported antibodies against CCHFV, providing the molecular underpinnings essential for developing CCHFV­specific medical countermeasures for epidemic preparedness.

Structural characterization of a pathogenic mutant of human protein tyrosine phosphatase PTPN2 (Cys216Gly) that causes very early onset autoimmune enteropathy.

PTPN2 is an important protein tyrosine phosphatase (PTP) that plays a key role in cell signaling. Deletions or inactivating mutations of PTPN2 have been described in different pathologies and underline its critical role in hematopoiesis, autoimmunity, and inflammation. Surprisingly, despite the major pathophysiological implications of PTPN2, the structural analysis of this PTP and notably of its pathogenic mutants remains poorly documented. Contrary to other human PTP enzymes, to date, only one structure of PTPN2 (wild-type form) has been reported. Here, we report the first crystal structure of a pathogenic mutant of PTPN2 (Cys216Gly) that causes an autoimmune enteropathy. We show in particular that this mutant adopts a classical PTP fold. More importantly, albeit inactive, the mutant retains its ability to bind substrates and to adopt the characteristic catalytically competent closed form of PTP enzymes. This novel PTPN2 structure may serve as a new tool to better understand PTP structures and the structural impacts of pathogenic mutations. Moreover, the C216G PTPN2 structure could also be helpful to design specific ligands/inhibitors.

The epitope arrangement on flavivirus particles contributes to Mab C10's extraordinary neutralization breadth across Zika and dengue viruses.

The human monoclonal antibody C10 exhibits extraordinary cross-reactivity, potently neutralizing Zika virus (ZIKV) and the four serotypes of dengue virus (DENV1-DENV4). Here we describe a comparative structure-function analysis of C10 bound to the envelope (E) protein dimers of the five viruses it neutralizes. We demonstrate that the C10 Fab has high affinity for ZIKV and DENV1 but not for DENV2, DENV3, and DENV4. We further show that the C10 interaction with the latter viruses requires an E protein conformational landscape that limits binding to only one of the three independent epitopes per virion. This limited affinity is nevertheless counterbalanced by the particle's icosahedral organization, which allows two different dimers to be reached by both Fab arms of a C10 immunoglobulin. The epitopes' geometric distribution thus confers C10 its exceptional neutralization breadth. Our results highlight the importance not only of paratope/epitope complementarity but also the topological distribution for epitope-focused vaccine design.