The cyanobacterial ribosomal-associated protein LrtA from Synechocystis sp. PCC 6803 is an oligomeric protein in solution with chameleonic sequence properties

The LrtA protein of Synechocystis sp. PCC 6803 intervenes in cyanobacterial post-stress survival and in stabilizing 70S ribosomal particles. It belongs to the hibernating promoting factor (HPF) family of proteins, involved in protein synthesis. In this work, we studied the conformational preferences and stability of isolated LrtA in solution. At physiological conditions, as shown by hydrodynamic techniques, LrtA was involved in a self-association equilibrium. As indicated by Nuclear Magnetic Resonance (NMR), circular dichroism (CD) and fluorescence, the protein acquired a folded, native-like conformation between pH 6.0 and 9.0. However, that conformation was not very stable, as suggested by thermal and chemical denaturations followed by CD and fluorescence. Theoretical studies of its highly-charged sequence suggest that LrtA had a Janus sequence, with a context-dependent fold. Our modelling and molecular dynamics (MD) simulations indicate that the protein adopted the same fold observed in other members of the HPF family ( - - - - - ) at its N-terminal region (residues 1–100), whereas the C terminus (residues 100–197) appeared disordered and collapsed, supporting the overall percentage of overall secondary structure obtained by CD deconvolution. Then, LrtA has a chameleonic sequence and it is the first member of the HPF family involved in a self-association equilibrium, when isolated in solution.Ministerio de Economía y Competitividad CTQ2015-64445-RMinisterio de Economía y Competitividad BIO2016-78020-RMinisterio de Economía y Competitividad FIS2014-52212-RMinisterio de Economía y Competitividad BIO2016-75634-PFundación Séneca 19353/PI/1

Premios Isabel Zendal de Promoción do Pensamento Crítico en Educación Secundaria e Bacharelato. I Edición

A I Edición dos Premios Isabel Zendal de Promoción do Pensamento Crítico en Educación Secundaria e Bacharelato foi convocada o 13 de marzo de 2019 pola Vicerreitoría de Estudantes, Participación e Extensión Universitaria da Universidade da Coruña.Corrección de erros: Tras a publicación destes premios, detectouse un erro material: na Categoría B, para o alumnado desde 4º curso de educación secundaria obrigatoria ata 2º de Bacharelato e ciclos formativos de grao medio, onde di “Claudia Hernández Suárez”, debería dicir “Claudia Hernández Suáñez

Human importin α3 and its N-terminal truncated form, without the importin-β-binding domain, are oligomeric species with a low conformational stability in solution

[Background]: Eukaryotic cells have a continuous transit of macromolecules between the cytoplasm and the nucleus. Several carrier proteins are involved in this transport. One of them is importin α, which must form a complex with importin β to accomplish its function, by domain-swapping its 60-residue-long N terminus. There are several human isoforms of importin α; among them, importin α3 has a particularly high flexibility.[Methods]: We studied the conformational stability of intact importin α3 (Impα3) and its truncated form, where the 64-residue-long, N-terminal importin-β-binding domain (IBB) has been removed (ΔImpα3), in a wide pH range, with several spectroscopic, biophysical, biochemical methods and with molecular dynamics (MD).[Results]: Both species acquired native-like structure between pH 7 and 10.0, where Impα3 was a dimer (with an apparent self-association constant of ~10 μM) and ΔImpα3 had a higher tendency to self-associate than the intact species. The acquisition of secondary, tertiary and quaternary structure, and the burial of hydrophobic patches, occurred concomitantly. Both proteins unfolded irreversibly at physiological pH, by using either temperature or chemical denaturants, through several partially folded intermediates. The MD simulations support the presence of these intermediates.[Conclusions]: The thermal stability of Impα3 at physiological pH was very low, but was higher than that of ΔImpα3. Both proteins were stable in a narrow pH range, and they unfolded at physiological pH populating several intermediate species.[General significance]: The low conformational stability explains the flexibility of Impα3, which is needed to carry out its recognition of complex cargo sequences.This work was supported by Spanish Ministry of Economy and Competitiveness and European FEDER Funds (MCIU/AEI/FEDER, EU) [RTI2018-097991-B-I00 to JLN and JG, BFU2016-75471-C2-1-P to CA, PGC2018-094548-B-I00 to AA and BIO2016-78020-R to ACA], Basque Country [IT-1175-19 to AA], GVA and EU-FEDER funds “Una forma de hacer Europa” [GVA-IDIFEDER 2018/020] and Portuguese FCT [UIDB/04565/2020 and SAICTPAC/0019/2015 to AC and MP]. AUC SV assays were performed at the Molecular Interactions Facility at the CIB Margarita Salas. CD-G acknowledges Medical Biochemistry and Biophysics Doctoral Programme (M2B-PhD) FCT reference: SFRH/PD/BD/135154/2017. BR acknowledges the kind hospitality and use of computational resources in the European Magnetic Resonance Center (CERM), Sesto Fiorentino (Florence), Italy.Peer reviewe