Biology subjects

Chaves-Sanjuan, A.

Publications and source records attributed to Chaves-Sanjuan, A..

6 recordsLinked to original sources

bioRxiv2025

Structural determinants for red-shifted absorption in higher-plants Photosystem I

- Higher plants Photosystem I absorbs near-infrared light through long-wavelength chlorophylls, enriched under vegetation canopies, to enhance photon capture. Far-red absorption originates from chlorophylls pairs within the Lhca3 and Lhca4 subunits of the LHCI antenna, known as the "red cluster" composed of chlorophylls a603 and a609. - We used reverse genetics to produce an Arabidopsis mutant devoid of red-shifted absorption, and we obtained high-resolution cryo-EM structures from purified PSI-LHCI complexes in both wild-type and mutant plants. - Computed excitonic coupling values suggested a possible contribution of additional nearby pigment molecules, namely chlorophyll a615 and violaxanthin in L2 site, to far-red absorption. Therefore, we investigated the structural determinants of far-red absorption and analyzed the spectroscopic effects of these additional pigments by producing further Arabidopsis transgenic lines. The two experimental structures were used for quantum mechanics calculations, revealing that excitonic interactions alone cannot explain far-red absorption, while charge transfer states were needed for accurate spectral simulations. - Our findings demonstrate that the molecular mechanisms of light-harvesting under shaded conditions rely on very precise tuning of chromophore interactions, an understanding of which is crucial for designing light-harvesting complexes with engineered absorption spectra

plant biology↗

bioRxiv2025

Structural bases for Nuclear Factor 1-X activation and DNA recognition. Prototypic insight into the NFI transcription factor family

Nuclear Factor I (NFI) proteins were first identified in adenovirus DNA replication and later as regulators of gene transcription, stem cell proliferation, and differentiation. They play key roles in development, cancer and congenital disorders. Within the NFI family, NFI-X is critical for neural stem cell biology, hematopoiesis, muscle development, muscular dystrophies and oncogenesis. Here, we present the first structural characterization of the NFI transcription factor, NFI-X, both alone and bound to its consensus palindromic DNA site. Our analyses reveal a novel, MH1-like fold within NFI-X DNA-binding domain (DBD) and identify crucial structural determinants for activity, such as a Zn{superscript 2} binding site, dimeric assembly, activation mechanism and DNA-binding specificity. Given the >95% sequence identity within the NFI DBDs, our structural data are prototypic for the entire family; a NFI Rosetta Stone that allows decoding a wealth of biochemical and functional data and provides a precise target for drug design in a wider disease context.

biochemistry↗

bioRxiv2023

THE RIBOREGULATION MECHANISM OF HUMAN SERINE HYDROXYMETHYLTRANSFERASE IS ROOTED IN AN ALLOSTERIC SWITCH

RNA can directly control protein activity in a process called riboregulation; only a few mechanisms of riboregulation have been described in detail, none of these being characterized on structural grounds. Here we present a comprehensive structural, functional, and phylogenetic analysis of riboregulation of cytosolic serine hydroxymethyltransferase (SHMT1), the enzyme interconverting serine and glycine in one-carbon metabolism. We show that the RNA modulator competes with polyglutamylated folates and acts as an allosteric switch, selectively altering the enzymes reactivity vs. serine. In addition, we identify the tetrameric assembly and a flap structural motif as key structural elements necessary for binding of RNA to eukaryotic SHMT1. The results presented here suggest that riboregulation may have played a role in the evolution of eukaryotic SHMT1 and the compartmentalization of one-carbon metabolism. The findings also provide insights for RNA-based therapeutic strategies targeting this cancer-linked metabolic pathway.

biochemistry↗

bioRxiv2022

Cryo-EM Structure of a Mammalian-specific Alternative Amyloid Exon

hnRNPDL is a ribonucleoprotein (RNP) involved in transcription and RNA-processing, with missense mutations causing limb-girdle muscular dystrophy-3 (LGMDD3). Mammalian-specific alternative splicing (AS) renders three natural isoforms, hnRNPDL-2 being predominant in humans. We present the cryo-electron microscopy structure of full-length hnRNPDL-2 amyloid fibrils, which are stable, non-toxic, and bind nucleic acids, with the RNA binding domains building a solenoidal coat around them. The amyloid core consists of a single Gly/Tyr-rich and highly hydrophilic filament containing internal water channels. The architecture and activity of hnRNPDL-2 fibrils are reminiscent of functional amyloids, our results suggesting that LGMDD3 might be a loss-of-function disease associated with impaired fibrillation. Strikingly, the fibril core matches exon 6, absent in the soluble hnRNPDL-3 isoform. This provides structural evidence for AS controlling hnRNPDL assembly by precisely including/skipping an amyloid exon, a mechanism that holds the potential to generate functional diversity in RNPs.

biochemistry↗

bioRxiv2022

Spike mutation resilient scFv76 antibody counteracts SARS-CoV-2 lung damage upon aerosol delivery

Uneven worldwide vaccination coverage against SARS-CoV-2 and emergence of variants escaping immunity call for broadly-effective and easily-deployable therapeutics. We previously described the human single-chain scFv76 antibody, which recognizes SARS-CoV-2 Alfa, Beta, Gamma and Delta variants. We now show that scFv76 also neutralizes infectivity and fusogenic activity of Omicron BA.1 and BA.2 variants. Cryo-EM analysis reveals that scFv76 binds to a well-conserved SARS-CoV-2 spike epitope, providing the structural basis for its broad-spectrum activity. Moreover, we demonstrate that nebulized scFv76 exhibits therapeutic efficacy in a severe hACE2 transgenic mouse model of COVID-19 pneumonia, as shown by body weight and pulmonary viral load data. Counteraction of infection correlates with the inhibition of lung inflammation observed by histopathology and expression of inflammatory cytokines and chemokines. Biomarkers of pulmonary endothelial damage were also significantly reduced in scFv76-treated mice. Altogether the results support the use of nebulized scFv76 for COVID-19 induced by any SARS-CoV-2 variants emerged so far.

microbiology↗

bioRxiv2022

Cryo-EM structure of ex vivo fibrils associated with extreme AA amyloidosis prevalence in a cat shelter

AA amyloidosis is a systemic disease characterized by deposition of misfolded serum amyloid A protein (SAA) into cross-{beta} amyloid in multiple organs in humans and animals. AA amyloidosis occurs at high SAA serum levels during chronic inflammation. The disease can be transmitted horizontally, likely facilitated by prion-like mechanism, in captive animals leading to extreme disease prevalence, e.g. 70% in captive cheetah and 57-73% in domestic short hair (DSH) cats kept in shelters. Herein, we present the 3.3 [A] cryo-EM structure of an AA amyloid extracted post-mortem from the kidney of a DSH cat with renal failure. The structure reveals a cross-{beta} architecture assembled from two 76-residue long proto-filaments. Despite >70% sequence homology to mouse and human SAA, the cat SAA variant adopts a distinct amyloid fold. Based on shared disease profiles and almost identical protein sequences, we propose a similar amyloid fold of deposits identified previously in captive cheetah.

biophysics↗