About the author Ana Garcia del Arco

CryoEM of RUVBL1–RUVBL2–ZNHIT2, a complex that interacts with pre-mRNA-processing-splicing factor 8

Marina Serna, Ana González-Corpas, Sofía Cabezudo, Andrés López-Perrote, Gianluca Degliesposti, Eduardo Zarzuela, J Mark Skehel, Javier Muñoz and Oscar Llorca

Abstract: Biogenesis of the U5 small nuclear ribonucleoprotein (snRNP) is an essential and highly regulated process. In particular, PRPF8, one of U5 snRNP main components, requires HSP90 working in concert with R2TP, a cochaperone complex containing RUVBL1 and RUVBL2 AAA-ATPases, and additional factors that are still poorly characterized. Here, we use biochemistry, interaction mapping, mass spectrometry and cryoEM to study the role of ZNHIT2 in the regulation of the R2TP chaperone during the biogenesis of PRPF8. ZNHIT2 forms a complex with R2TP which depends exclusively on the direct interaction of ZNHIT2 with the RUVBL1–RUVBL2 ATPases. The cryoEM analysis of this complex reveals that ZNHIT2 alters the conformation and nucleotide state of RUVBL1–RUVBL2, affecting its ATPase activity. We characterized the interactions between R2TP, PRPF8, ZNHIT2, ECD and AAR2 proteins. Interestingly, PRPF8 makes a direct interaction with R2TP and this complex can incorporate ZNHIT2 and other proteins involved in the biogenesis of PRPF8 such as ECD and AAR2. Together, these results show that ZNHIT2 participates in the assembly of the U5 snRNP as part of a network of contacts between assembly factors required for PRPF8 biogenesis and the R2TP-HSP90 chaperone, while concomitantly regulating the structure and nucleotide state of R2TP.

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Molecular Recognition by Silicon Nanowire Field-Effect Transistor and Single-Molecule Force Spectroscopy

Francisco M. Espinosa, Manuel R. Uhlig and Ricardo Garcia.

Abstract: Silicon nanowire (SiNW) field-effect transistors (FETs) have been developed as very sensitive and label-free biomolecular sensors. The detection principle operating in a SiNW biosensor is indirect. The biomolecules are detected by measuring the changes in the current through the transistor. Those changes are produced by the electrical field created by the biomolecule. Here, we have combined nanolithography, chemical functionalization, electrical measurements and molecular recognition methods to correlate the current measured by the SiNW transistor with the presence of specific molecular recognition events on the surface of the SiNW. Oxidation scanning probe lithography (o-SPL) was applied to fabricate sub-12 nm SiNW field-effect transistors. The devices were applied to detect very small concentrations of proteins (500 pM). Atomic force microscopy (AFM) single-molecule force spectroscopy (SMFS) experiments allowed the identification of the protein adsorption sites on the surface of the nanowire. We detected specific interactions between the biotin-functionalized AFM tip and individual avidin molecules adsorbed to the SiNW. The measurements confirmed that electrical current changes measured by the device were associated with the deposition of avidin molecules.

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Accurate Wide-Modulus-Range Nanomechanical Mapping of Ultrathin Interfaces with Bimodal Atomic Force Microscopy

Victor G. Gisbert and Ricardo Garcia

Abstract: The nanoscale determination of the mechanical properties of interfaces is of paramount relevance in materials science and cell biology. Bimodal atomic force microscopy (AFM) is arguably the most advanced nanoscale method for mapping the elastic modulus of interfaces. Simulations, theory, and experiments have validated bimodal AFM measurements on thick samples (from micrometer to millimeter). However, the bottom-effect artifact, this is, the influence of the rigid support on the determination of the Young’s modulus, questions its accuracy for ultrathin materials and interfaces (1–15 nm). Here we develop a bottom-effect correction method that yields the intrinsic Young’s modulus value of a material independent of its thickness. Experiments and numerical simulations validate the accuracy of the method for a wide range of materials (1 MPa to 100 GPa). Otherwise, the Young’s modulus of an ultrathin material might be overestimated by a 10-fold factor.

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Structural basis for substrate specificity of heteromeric transporters of neutral amino acids

Carlos F. RodriguezPaloma Escudero-BravoLucía DíazPaola BartoccioniCarmen García-MartínJoan G. GilabertJasminka BoskovicVíctor GuallarEkaitz Errasti-MurugarrenOscar Llorca and Manuel Palacín.

Abstract: Despite having similar structures, each member of the heteromeric amino acid transporter (HAT) family shows exquisite preference for the exchange of certain amino acids. Substrate specificity determines the physiological function of each HAT and their role in human diseases. However, HAT transport preference for some amino acids over others is not yet fully understood. Using cryo–electron microscopy of apo human LAT2/CD98hc and a multidisciplinary approach, we elucidate key molecular determinants governing neutral amino acid specificity in HATs. A few residues in the substrate-binding pocket determine substrate preference. Here, we describe mutations that interconvert the substrate profiles of LAT2/CD98hc, LAT1/CD98hc, and Asc1/CD98hc. In addition, a region far from the substrate-binding pocket critically influences the conformation of the substrate-binding site and substrate preference. This region accumulates mutations that alter substrate specificity and cause hearing loss and cataracts. Here, we uncover molecular mechanisms governing substrate specificity within the HAT family of neutral amino acid transporters and provide the structural bases for mutations in LAT2/CD98hc that alter substrate specificity and that are associated with several pathologies.

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The Bacterial Mucosal Immunotherapy MV130 Protects Against SARS-CoV-2 Infection and Improves COVID-19 Vaccines Immunogenicity

Carlos del Fresno, Juan García-Arriaza, Sarai Martínez-Cano, Ignacio Heras-Murillo, Aitor Jarit-Cabanillas, Joaquín Amores-Iniesta, Paola Brandi, Gillian Dunphy, Carmen Suay-Corredera, Maria Rosaria Pricolo, Natalia Vicente, Andrés López-Perrote, Sofía Cabezudo, Ana González-Corpas, Oscar Llorca, Jorge Alegre-Cebollada, Urtzi Garaigorta, Pablo Gastaminza, Mariano Esteban, and David Sancho.

Abstract: COVID-19-specific vaccines are efficient prophylactic weapons against SARS-CoV-2 virus. However, boosting innate responses may represent an innovative way to immediately fight future emerging viral infections or boost vaccines. MV130 is a mucosal immunotherapy, based on a mixture of whole heat-inactivated bacteria, that has shown clinical efficacy against recurrent viral respiratory infections. Herein, we show that the prophylactic intranasal administration of this immunotherapy confers heterologous protection against SARS-CoV-2 infection in susceptible K18-hACE2 mice. Furthermore, in C57BL/6 mice, prophylactic administration of MV130 improves the immunogenicity of two different COVID-19 vaccine formulations targeting the SARS-CoV-2 spike (S) protein, inoculated either intramuscularly or intranasally. Independently of the vaccine candidate and vaccination route used, intranasal prophylaxis with MV130 boosted S-specific responses, including CD8+-T cell activation and the production of S-specific mucosal IgA antibodies. Therefore, the bacterial mucosal immunotherapy MV130 protects against SARS-CoV-2 infection and improves COVID-19 vaccines immunogenicity.

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CDK1 and PLK1 cooperate to regulate BICD2, dynein activation and recruitment to the nucleus as well as centrosome separation in G2/M

Núria Gallisà-Suñé, Paula Sànchez-Fernàndez-de-Landa, Fabian Zimmermann, Marina Serna, Joel Paz, Laura Regué, Oscar Llorca, Jens Lüders and Joan Roig

Abstract: The activity of dynein is regulated by a number of adaptors that mediate its interaction with dynactin, effectively activating the motor complex while also connecting it to different cargos. The regulation of adaptors is consequently central to dynein physiology, but remains largely unexplored. We now describe that one of the bestknown dynein adaptors, BICD2, is effectively activated through phosphorylation. In G2 phosphorylation of BICD2 by CDK1 promotes its interaction with PLK1. In turn, PLK1 phosphorylation of a single residue in the N-terminus of BICD2 results in a conformational change that facilitates interaction with dynein and dynactin, allowing the formation of active motor complexes. BICD2 phosphorylation is central for dynein recruitment to the nuclear envelope, centrosome tethering to the nucleus and centrosome separation in G2/M. This work reveals adaptor activation through phosphorylation as crucial for the spatiotemporal regulation of dynein activity.

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