Biology subjects

Mas, C.

Publications and source records attributed to Mas, C..

4 recordsLinked to original sources

bioRxiv2026

Structural modelling and functional analysis support lipid binding by the dimeric E. coli DedA protein YqjA

Maintenance of membrane homeostasis is essential for bacterial viability, yet the molecular functions of many membrane proteins involved in this process remain poorly understood. The widely distributed DedA superfamily of integral membrane proteins has been implicated in membrane homeostasis, with deletion of DedA genes resulting in sensitivities to temperature, pH and a range of antimicrobial compounds. Several bacterial DedA proteins have been linked to lipid transport, providing a potential connection between function and phenotype. However, a lack of direct functional and structural data means that the precise role of DedA proteins in bacterial membrane homeostasis remains unclear. Here, using analytical ultracentrifugation (AUC), we show that the Escherichia coli DedA protein YqjA exists predominantly as a dimer and, by combining structural modelling with site-specific cysteine crosslinking, we have identified the most likely dimer interface. Modelling of dimeric YqjA in the presence of lipids predicts an interfacial lipid-binding site located in close proximity to several conserved, functionally important residues. Consistent with lipid binding, addition of lipid substantially increased the thermal stability of YqjA. Furthermore, mutation of residues associated with the predicted binding site impaired YqjA function. Together, these findings provide new structural and functional insights into the DedA family and support a role for lipid binding in the activity of YqjA.

biochemistry↗

bioRxiv2026

Superinfection exclusion strategy of siphophage T5: analysis of the FhuA:Llp complex

Superinfection exclusion is a widespread viral mechanism that protects the infected cell from over infection by other, identical or closely related viruses. Shortly after infection by bac-teriophage T5, the bacterium E. coli produces Llp coded by the just injected viral genome. Llp is a small lipoprotein targeted to the inner-leaflet of the host outer-membrane. It binds to FhuA, an outer-membrane iron-ferrichrome transporter, which is T5 receptor at the E. coli cell surface. The interaction between Llp and FhuA prevents any further bacteriophage binding and infection. Here, we determined the RMN structure of Llp and analyse the formation of the FhuA:Llp complex using a wide range of techniques and mutants, both in vivo and in vitro. Interaction of Llp to FhuA is governed by a two-step equilibrium with a strong contribution of induced fit: Llp binding requires remodelling of FhuA periplasmic plug surface, allowing the further large conformational reorganisation of the extracellular loops. Analysis of FhuA mu-tants show the importance of the intertwined interactions between the extracellular loops and the plug in the communication between the periplasmic and the extracellular faces of FhuA.

biophysics↗

bioRxiv2025

Hydra domain drives SNF2L multimerization and marks ISWI diversification in parasites

ISWI chromatin remodelers are conserved regulators of nucleosome positioning and chromatin accessibility across eukaryotes, yet their evolutionary diversification is poorly understood. In the apicomplexan parasite Toxoplasma gondii, we identify Hydra, a previously unrecognized globular domain embedded within TgSNF2L, one of two ISWI paralogues. Hydra is structurally unique, lacking homology to any known protein fold, and represents a lineage-specific insertion in an otherwise structurally conserved protein family. Biochemical analyses reveal that the isolated Hydra domain self-assembles into stable oligomers, undergoing reversible equilibrium with its monomeric form. Cryo-electron microscopy analysis reveals discrete globular assemblies, though little consistency could be obtained, suggesting a highly dynamic complex. Deletion of Hydra from full-length TgSNF2L disrupts its intrinsic ability to form higher order oligomers in solution, yielding predominantly monomeric and dimeric species. Functionally, the Hydra-driven multimerization of TgSNF2L modulates its availability for chromatin engagement in response to cell-cycle cues. Hydra thus represents the first reported structural innovation within the ISWI family.

molecular biology↗

bioRxiv2025

Analytical Ultracentrifugation as a Tool for Exploring COSAN Assemblies.

The self-assembly of the cobalta bis(dicarbollide) (COSAN) anionic boron clusters into micelles above a critical micelle concentration (cmc) of 10 - 20 mM and its behavior as "sticky nano-ions" facilitating controlled protein aggregation have been previously investigated using scattering techniques, particularly small-angle neutron and X-ray scattering. These techniques effectively provide average structural parameters but, when applied to colloidal systems, often rely on models assuming polydispersity or anisotropic shapes. Thus, complementary techniques are required to confirm or infirm the proposed analyses. Here, we employed sedimentation velocity analytical ultracentrifugation (SV-AUC), which offers the ability to resolve discrete species. We revisited two key questions: (1) the aggregation behavior of COSAN into micelles, a topic still under debate and due to its unconventional amphiphilic nature, and (2) the nature of the protein assemblies induced by COSAN, specifically their size/shape distribution and aggregation number. Our findings confirm the cmc of COSAN of 16 mM and reveal that COSAN micelles exhibit low aggregation numbers (8 in water and 14 in dilute salt), consistent with recent hypotheses. Furthermore, SV-AUC showed that COSAN promotes myoglobin aggregation into discrete oligomeric species with well-defined aggregation numbers, such as dimers, tetramers, and higher-order assemblies, depending on the COSAN-to-protein ratio. These results provide clarity on the discrete nature of COSAN micelle aggregation and protein assembly. This study highlights the complementary role of SV-AUC in understanding supramolecular assemblies, offering useful insights into the behavior of COSAN nano-ions and their interactions with biomacromolecules.

biophysics↗