Deglycosylated RBD produced in Pichia pastoris as a low-cost sera COVID-19 diagnosis tool and a vaccine candidate.

During the COVID-19 outbreak, numerous tools including protein-based vaccines have been developed. The methylotrophic yeast Pichia pastoris (synonymous to Komagataella phaffii) is an eukaryotic cost-effective and scalable system for recombinant protein production, with the advantages of an efficient secretion system and the protein folding assistance of the secretory pathway of eukaryotic cells. In a previous work, we compared the expression of SARS-CoV-2 Spike Receptor Binding Domain in P. pastoris with that in human cells. Although the size and glycosylation pattern was different between them, their protein structural and conformational features were indistinguishable. Nevertheless, since high mannose glycan extensions in proteins expressed by yeast may be the cause of a nonspecific immune recognition, we deglycosylated RBD in native conditions. This resulted in a highly pure, homogenous, properly folded and monomeric stable protein. This was confirmed by circular dichroism and tryptophan fluorescence spectra and by SEC-HPLC, which were similar to those of RBD proteins produced in yeast or human cells. Deglycosylated RBD was obtained at high yields in a single step, and it was efficient in distinguishing between SARS-CoV-2-negative and positive sera from patients. Moreover, when the deglycosylated variant was used as an immunogen, it elicited a humoral immune response ten times greater than the glycosylated form, producing antibodies with enhanced neutralizing power and eliciting a more robust cellular response. The proposed approach may be used to produce at a low cost, many antigens that require glycosylation to fold and express, but do not require glycans for recognition purposes.

Structural basis for the Pr-Pfr long-range signaling mechanism of a full-length bacterial phytochrome at the atomic level.

Phytochromes constitute a widespread photoreceptor family that typically interconverts between two photostates called Pr (red light­absorbing) and Pfr (far-red light­absorbing). The lack of full-length structures solved at the (near-)atomic level in both pure Pr and Pfr states leaves gaps in the structural mechanisms involved in the signal transmission pathways during the photoconversion. Here, we present the crystallographic structures of three versions from the plant pathogen Xanthomonas campestris virulence regulator XccBphP bacteriophytochrome, including two full-length proteins, in the Pr and Pfr states. The structures show a reorganization of the interaction networks within and around the chromophore-binding pocket, an α-helix/ß-sheet tongue transition, and specific domain reorientations, along with interchanging kinks and breaks at the helical spine as a result of the photoswitching, which subsequently affect the quaternary assembly. These structural findings, combined with multidisciplinary studies, allow us to describe the signaling mechanism of a full-length bacterial phytochrome at the atomic level.

Pr-favoured variants of the bacteriophytochrome from the plant pathogen Xanthomonas campestris hint on light regulation of virulence-associated mechanisms.

Red/far-red light-sensing bacteriophytochrome photoreceptor (BphP) pathways play key roles in bacterial physiology and ecology. These bilin-binding proteins photoswitch between two states, Pr (red absorbing) and Pfr (far-red absorbing). The isomerization of the chromophore and the downstream structural changes result in the light signal transduction. The agricultural pathogen Xanthomonas campestris pv. campestris (Xcc) code for a single bathy-like type BphP (XccBphP), previously shown to negatively regulate several light-mediated biological processes involved in virulence. Here, we generated three different full-length variants with single amino acid changes within its GAF domain that affect the XccBphP photocycle favouring its Pr state: L193Q, L193N and D199A. While D199A recombinant protein locks XccBphP in a Pr-like state, L193Q and L193N exhibit a significant enrichment of the Pr form in thermal equilibrium. The X-ray crystal structures of the three variants were solved, resembling the wild-type protein in the Pr state. Finally, we studied the effects of altering the XccBphP photocycle on the exopolysaccharide xanthan production and stomatal aperture assays as readouts of its bacterial signalling pathway. Null-mutant complementation assays show that the photoactive Pr-favoured XccBphP variants L193Q and L193N tend to negatively regulate xanthan production in vivo. In addition, our results indicate that strains expressing these variants also promote stomatal apertures in challenged plant epidermal peels, compared to wild-type Xcc. The findings presented in this work provide new evidence on the Pr state of XccBphP as a negative regulator of the virulence-associated mechanisms by light in Xcc.

Development of a Reverse Genetic System to Generate Recombinant Chimeric Tacaribe Virus that Expresses Junín Virus Glycoproteins.

Mammarenaviruses are enveloped and segmented negative-stranded RNA viruses that comprise several pathogenic members associated with severe human hemorrhagic fevers. Tacaribe virus (TCRV) is the prototype for the New World group of mammarenaviruses and is not only naturally attenuated but also phylogenetically and antigenically related to all South American pathogenic mammarenaviruses, particularly the Junín virus (JUNV), which is the etiological agent of Argentinian hemorrhagic fever (AHF). Moreover, since TCRV protects guinea pigs and non-human primates from lethal challenges with pathogenic strains of JUNV, it has already been considered as a potential live-attenuated virus vaccine candidate against AHF. Here, we report the development of a reverse genetic system that relies on T7 polymerase-driven intracellular expression of the complementary copy (antigenome) of both viral S and L RNA segments. Using this approach, we successfully recovered recombinant TCRV (rTCRV) that displayed growth properties resembling those of authentic TCRV. We also generated a chimeric recombinant TCRV expressing the JUNV glycoproteins, which propagated similarly to wild-type rTCRV. Moreover, a controlled modification within the S RNA 5' non-coding terminal sequence diminished rTCRV propagation in a cell-type dependent manner, giving rise to new perspectives where the incorporation of additional attenuation markers could contribute to develop safe rTCRV-based vaccines against pathogenic mammarenaviruses.

Development of a hyperimmune equine serum therapy for COVID-19 in Argentina.

The disease named COVID-19, caused by the SARS-CoV-2 coronavirus, is currently generating a global pandemic. Vaccine development is no doubt the best long-term immunological approach, but in the current epidemiologic and health emergency there is a need for rapid and effective solutions. Convalescent plasma is the only antibody-based therapy available for COVID-19 patients to date. Equine polyclonal antibodies (EpAbs) put forward a sound alternative. The new generation of processed and purified EpAbs containing highly purified F(ab')2 fragments demonstrated to be safe and well tolerated. EpAbs are easy to manufacture allowing a fast development and scaling up for a treatment. Based on these ideas, we present a new therapeutic product obtained after immunization of horses with the receptor-binding domain of the viral Spike glycoprotein. Our product shows around 50 times more potency in in vitro seroneutralization assays than the average of convalescent plasma. This result may allow us to test the safety and efficacy of this product in a phase 2/3 clinical trial to be conducted in July 2020 in the metropolitan area of Buenos Aires, Argentina.

La enfermedad denominada COVID-19 es causada por el coronavirus SARS-CoV-2 y es actualmente considerada una pandemia a nivel global. El desarrollo de vacunas es sin duda la mejor estrategia a largo plazo, pero debido a la emergencia sanitaria, existe una necesidad urgente de encontrar soluciones rápidas y efectivas para el tratamiento de la enfermedad. Hasta la fecha, el uso de plasma de convalecientes es la única inmunoterapia disponible para pacientes hospitalizados con COVID-19. El uso de anticuerpos policlonales equinos (EpAbs) es otra alternativa terapéutica interesante. La nueva generación de EpAbs incluyen el procesamiento y purificación de los mismos y la obtención de fragmentos F(ab')2 con alta pureza y un excelente perfil de seguridad en humanos. Los EpAbs son fáciles de producir, lo cual permite el desarrollo rápido y la elaboración a gran escala de un producto terapéutico. En este trabajo mostramos el desarrollo de un suero terapéutico obtenido luego de la inmunización de caballos utilizando el receptor-binding domain de la glicoproteína Spike del virus. Nuestro producto mostró ser alrededor de 50 veces más potente en ensayos de seroneutralización in vitro que el promedio de los plasmas de convalecientes. Estos resultados nos permitirían testear la seguridad y eficacia de nuestro producto en ensayos clínicos de fase 2/3 a realizarse a partir de julio de 2020 en la zona metropolitana de Buenos Aires, Argentina.

Development of a hyperimmune equine serum therapy for COVID-19 in Argentina

The disease named COVID-19, caused by the SARS-CoV-2 coronavirus, is currently generating a global pandemic. Vaccine development is no doubt the best long-term immunological approach, but in the current epidemiologic and health emergency there is a need for rapid and effective solutions. Convalescent plasma is the only antibody-based therapy available for COVID-19 patients to date. Equine polyclonal antibodies (EpAbs) put forward a sound alternative. The new generation of processed and purified EpAbs containing highly purified F(ab’)2 fragments demonstrated to be safe and well tolerated. EpAbs are easy to manufacture allowing a fast development and scaling up for a treatment. Based on these ideas, we present a new therapeutic product obtained after immunization of horses with the receptor-binding domain of the viral Spike glycoprotein. Our product shows around 50 times more potency in in vitro seroneutralization assays than the average of convalescent plasma. This result may allow us to test the safety and efficacy of this product in a phase 2/3 clinical trial to be conducted in July 2020 in the metropolitan area of Buenos Aires, Argentina.

La enfermedad denominada COVID-19 es causada por el coronavirus SARS-CoV-2 y es actualmente considerada una pandemia a nivel global. El desarrollo de vacunas es sin duda la mejor estrategia a largo plazo, pero debido a la emergencia sanitaria, existe una necesidad urgente de encontrar soluciones rápidas y efectivas para el tratamiento de la enfermedad. Hasta la fecha, el uso de plasma de convalecientes es la única inmunoterapia disponible para pacientes hospitalizados con COVID-19. El uso de anticuerpos policlonales equinos (EpAbs) es otra alternativa terapéutica interesante. La nueva generación de EpAbs incluyen el procesamiento y purificación de los mismos y la obtención de fragmentos F(ab’)2 con alta pureza y un excelente perfil de seguridad en humanos. Los EpAbs son fáciles de producir, lo cual permite el desarrollo rápido y la elaboración a gran escala de un producto terapéutico. En este trabajo mostramos el desarrollo de un suero terapéutico obtenido luego de la inmunización de caballos utilizando el receptor-binding domain de la glicoproteína Spike del virus. Nuestro producto mostró ser alrededor de 50 veces más potente en ensayos de seroneutralización in vitro que el promedio de los plasmas de convalecientes. Estos resultados nos permitirían testear la seguridad y eficacia de nuestro producto en ensayos clínicos de fase 2/3 a realizarse a partir de julio de 2020 en la zona metropolitana de Buenos Aires, Argentina.

DDX3 suppresses type I interferons and favors viral replication during Arenavirus infection.

Several arenaviruses cause hemorrhagic fever (HF) diseases that are associated with high morbidity and mortality in humans. Accordingly, HF arenaviruses have been listed as top-priority emerging diseases for which countermeasures are urgently needed. Because arenavirus nucleoprotein (NP) plays critical roles in both virus multiplication and immune-evasion, we used an unbiased proteomic approach to identify NP-interacting proteins in human cells. DDX3, a DEAD-box ATP-dependent-RNA-helicase, interacted with NP in both NP-transfected and virus-infected cells. Importantly, DDX3 deficiency compromised the propagation of both Old and New World arenaviruses, including the HF arenaviruses Lassa and Junin viruses. The DDX3 role in promoting arenavirus multiplication associated with both a previously un-recognized DDX3 inhibitory role in type I interferon production in arenavirus infected cells and a positive DDX3 effect on arenavirus RNA synthesis that was dependent on its ATPase and Helicase activities. Our results uncover novel mechanisms used by arenaviruses to exploit the host machinery and subvert immunity, singling out DDX3 as a potential host target for developing new therapies against highly pathogenic arenaviruses.

Role of the ERK1/2 Signaling Pathway in the Replication of Junín and Tacaribe Viruses.

We have previously shown that the infection of cell cultures with the arenaviruses Junín (JUNV), Tacaribe (TCRV), and Pichindé promotes the phosphorylation of mitogen-activated protein kinases (MAPKs) extracellular signal-regulated kinases 1 and 2 (ERK1/2) and that this activation is required for the achievement of a productive infection. Here we examined the contribution of ERK1/2 in early steps of JUNV and TCRV multiplication. JUNV adsorption, internalization, and uncoating were not affected by treatment of cultured cells with U0126, an inhibitor of the ERK1/2 signaling pathway. In contrast, U0126 caused a marked reduction in viral protein expression and RNA synthesis, while JUNV RNA synthesis was significantly augmented in the presence of an activator of the ERK1/2 pathway. Moreover, U0126 impaired the expression of a reporter gene in a TCRV-based replicon system, confirming the ability of the compound to hinder arenavirus macromolecular synthesis. By using a cell-based assay, we determined that the inhibitor did not affect the translation of a synthetic TCRV-like mRNA. No changes in the phosphorylation pattern of the translation factor eIF2α were found in U0126-treated cells. Our results indicate that U0126 impairs viral RNA synthesis, thereby leading to a subsequent reduction in viral protein expression. Thus, we conclude that ERK1/2 signaling activation is required for an efficient arenavirus RNA synthesis.

Regulation of Tacaribe Mammarenavirus Translation: Positive 5' and Negative 3' Elements and Role of Key Cellular Factors.

Mammarenaviruses are enveloped viruses with a bisegmented negative-stranded RNA genome that encodes the nucleocapsid protein (NP), the envelope glycoprotein precursor (GPC), the RNA polymerase (L), and a RING matrix protein (Z). Viral proteins are synthesized from subgenomic mRNAs bearing a capped 5' untranslated region (UTR) and lacking 3' poly(A) tail. We analyzed the translation strategy of Tacaribe virus (TCRV), a prototype of the New World mammarenaviruses. A virus-like transcript that carries a reporter gene in place of the NP open reading frame and transcripts bearing modified 5' and/or 3' UTR were evaluated in a cell-based translation assay. We found that the presence of the cap structure at the 5' end dramatically increases translation efficiency and that the viral 5' UTR comprises stimulatory signals while the 3' UTR,specifically the presence of a terminal C+G-rich sequence and/or a stem-loop structure, down-modulates translation. Additionally, translation was profoundly reduced in eukaryotic initiation factor (eIF) 4G-inactivated cells, whereas depletion of intracellular levels of eIF4E had less impact on virus-like mRNA translation than on a cell-like transcript. Translation efficiency was independent of NP expression or TCRV infection. Our results indicate that TCRV mRNAs are translated using a cap-dependent mechanism, whose efficiency relies on the interplay between stimulatory signals in the 5' UTR and a negative modulatory element in the 3' UTR. The low dependence on eIF4E suggests that viral mRNAs may engage yet-unknown noncanonical host factors for a cap-dependent initiation mechanism.IMPORTANCE Several members of the Arenaviridae family cause serious hemorrhagic fevers in humans. In the present report, we describe the mechanism by which Tacaribe virus, a prototypic nonpathogenic New World mammarenavirus, regulates viral mRNA translation. Our results highlight the impact of untranslated sequences and key host translation factors on this process. We propose a model that explains how viral mRNAs outcompete cellular mRNAs for the translation machinery. A better understanding of the mechanism of translation regulation of this virus can provide the bases for the rational design of new antiviral tools directed to pathogenic arenaviruses.

Differential contributions of tacaribe arenavirus nucleoprotein N-terminal and C-terminal residues to nucleocapsid functional activity.

UNLABELLED: The arenavirus nucleoprotein (NP) is the main protein component of viral nucleocapsids and is strictly required for viral genome replication mediated by the L polymerase. Homo-oligomerization of NP is presumed to play an important role in nucleocapsid assembly, albeit the underlying mechanism and the relevance of NP-NP interaction in nucleocapsid activity are still poorly understood. Here, we evaluate the contribution of the New World Tacaribe virus (TCRV) NP self-interaction to nucleocapsid functional activity. We show that alanine substitution of N-terminal residues predicted to be available for NP-NP interaction strongly affected NP self-association, as determined by coimmunoprecipitation assays, produced a drastic inhibition of transcription and replication of a TCRV minigenome RNA, and impaired NP binding to RNA. Mutagenesis and functional analysis also revealed that, while dispensable for NP self-interaction, key amino acids at the C-terminal domain were essential for RNA synthesis. Furthermore, mutations at these C-terminal residues rendered NP unable to bind RNA both in vivo and in vitro but had no effect on the interaction with the L polymerase. In addition, while all oligomerization-defective variants tested exhibited unaltered capacities to sustain NP-L interaction, NP deletion mutants were fully incompetent to bind L, suggesting that, whereas NP self-association is dispensable, the integrity of both the N-terminal and C-terminal domains is required for binding the L polymerase. Overall, our results suggest that NP self-interaction mediated by the N-terminal domain may play a critical role in TCRV nucleocapsid assembly and activity and that the C-terminal domain of NP is implicated in RNA binding. IMPORTANCE: The mechanism of arenavirus functional nucleocapsid assembly is still poorly understood. No detailed information is available on the nucleocapsid structure, and the regions of full-length NP involved in binding to viral RNA remain to be determined. In this report, novel findings are provided on critical interactions between the viral ribonucleoprotein components. We identify several amino acid residues in both the N-terminal and C-terminal domains of TCRV NP that differentially contribute to NP-NP and NP-RNA interactions and analyze their relevance for binding of NP to the L polymerase and for nucleocapsid activity. Our results provide insight into the contribution of NP self-interaction to RNP assembly and activity and reveal the involvement of the NP C-terminal domain in RNA binding.

Molecular determinants of arenavirus Z protein homo-oligomerization and L polymerase binding.

The arenavirus Z is a zinc-binding RING protein that has been implicated in multiple functions during the viral life cycle. These roles of Z involve interactions with viral and cellular proteins that remain incompletely understood. In this regard, Z inhibits viral RNA transcription and replication through direct interaction with the viral L polymerase. Here, we defined the L-binding domain of Tacaribe virus (TCRV) Z protein and the structural requirements mediating Z homo-oligomerization. By using site-directed mutagenesis, coimmunoprecipitation, and functional assays, we showed that residues R37, N39, W44, L50, and Y57, located around the zinc coordination site I, play a critical role in the Z-L interaction. We also found that Z protein from either TCRV or the pathogenic Junin virus (JUNV) self-associates into oligomeric forms in mammalian cells. Importantly, mutation of the myristoylation site, the strictly conserved residue G at position 2, severely impaired the ability of both TCRV Z and JUNV Z to self-interact as well as their capacity to accumulate at the plasma membrane, strongly suggesting that Z homo-oligomerization is associated with its myristoylation and cell membrane targeting. In contrast, disruption of the RING structure or substitution of W44 or N39, which are critical for L protein recognition, did not affect Z self-binding. Overall, the data presented here indicate that homo-oligomerization is not a requirement for Z-L interaction or Z-mediated polymerase activity inhibition.

HNF1 alpha gene coding regions mutations screening, in a Caucasian population clinically characterized as MODY from Argentina.

INTRODUCTION: There are at least six subtypes of Maturity Onset Diabetes of the Young (MODY) with distinctive genetic causes. MODY 3 is caused by mutations in HNF1A gene, an insulin transcription factor, so mutations in this gene are associated with impaired insulin secretion. MODY 3 prevalence differs according to the population analyzed, but it is one of the most frequent subtypes. Therefore, our aims in this work were to find mutations present in the HNF1A gene and provide information on their prevalence. MATERIAL AND METHODS: Mutations screening was done in a group of 80 unrelated patients (average age 17.1 years) selected by clinical characterization of MODY, by SSCP electrophoresis followed by sequenciation. RESULTS: We found eight mutations, of which six were novel and four sequence variants, which were all novel. Therefore the prevalence of MODY 3 in this group was 10%. Compared clinical data between the non-MODY 3 patients and the MODY 3 diagnosed patients did not show any significant difference. DISCUSSION: Eight patients were diagnosed as MODY 3 and new data about the prevalence of that subtype is provided. Our results contribute to reveal novel mutations, providing new data about the prevalence of that subtype.