Biology subjects

Martinez-del-Pozo, A.

Publications and source records attributed to Martinez-del-Pozo, A..

4 recordsLinked to original sources

bioRxiv2025

Recombinant production in Escherichia coli of functionally active alpha-hemolysin from the human pathogen Staphylococcus aureus

Staphylococcus aureus is a human opportunistic pathogen capable of causing multiple infections in both humans and animals. It secretes a group of exotoxins, known as hemolysins, which are released to enhance its pathogenicity. All of them exhibit cytolytic activity on a variety of host cell types, but -hemolysin stands out for being the most thoroughly studied variant. In this work, we show the production and purification of S. aureus -hemolysin following a straightforward protocol and in sufficient quantity to consider it as a potential procedure for future biotechnological approaches. Functional and structural characterization has indeed revealed that the protein is fully functional, confirming the key role of cholesterol in the necessary protein-lipid interaction. Furthermore, it has also been shown that the purified toxin can be assembled into single-particle individual pores within soluble lipid platforms in the form of cholesterol-containing nanodiscs.

biochemistry↗

bioRxiv2024

The action mechanism of actinoporins revealed through the structure of pore-forming intermediates

Pore-forming proteins exemplify the transformative potential of biological molecules. Initially produced in a monomeric, water-soluble form, they spontaneously assemble into multimeric integral membrane proteins in the presence of suitable target lipids. Their functions include roles in apoptosis, cell signaling, immunity, as well as attack and defense systems between different organisms. This latter group encompasses actinoporins, a family of pore-forming toxins from sea anemones that kill target cells by perforating their plasma membrane. Here, we have determined the structures of two such toxins, fragaceatoxin C and sticholysin II, in a membrane environment using cryogenic electron microscopy. The structures reveal how dozens of lipid molecules interact in an orderly manner, forming an intrinsic part of the pore. We have also isolated different pore-forming intermediates, where only a fraction of the constituent monomers is incorporated, exhibiting non-closed, arc-shaped structures. Based on these structures we propose a mechanism of action where the sequential assembly of toxin monomers onto the membrane, accompanied by conformational changes, triggers pore formation and membrane perforation. Our results contribute to a better understanding of the transforming capacity of these pore-forming proteins, which are becoming increasingly important for their diverse biotechnological applications.

biochemistry↗

bioRxiv2022

Cell response to extracellular matrix energy dissipation outweighs rigidity sensing

The mechanical properties of the extracellular matrix (ECM) determine cell differentiation, proliferation and migration through mechanoresponsive proteins including YAP. However, how different mechanical signals cooperate, synergize or compete to steer cell behavior remains poorly understood. Here, we have examined competition between the two major ECM mechanical cues, i.e. rigidity, which activates cell mechanosensing, and viscous energy dissipation, which reduces stiffness blunting cell mechanotransduction. To trigger competition, we have engineered protein hydrogels allowing concomitant modulation of stiffness and viscosity by mechanisms characteristic of native ECM. Culturing cells on these hydrogels, we have found that substrate energy dissipation attenuates YAP mechanosensing prevailing over stiffness cues. Hampered YAP activation on more dissipative substrates correlates with faster actin flow and smaller focal adhesions. Mechanistically, inhibition of actomyosin contractility reverses the outcome of the competition between rigidity and energy dissipation. Our results highlight the dominating contribution of substrate viscosity to the biology of the cell.

bioengineering↗

bioRxiv2018

Mitochondrial Na+ import controls oxidative phosphorylation and hypoxic redox signalling

All metazoans depend on O2 delivery and consumption by the mitochondrial oxidative phosphorylation (OXPHOS) system to produce energy. A decrease in O2 availability (hypoxia) leads to profound metabolic rewiring. In addition, OXPHOS uses O2 to produce reactive oxygen species (ROS) that can drive cell adaptations through redox signalling, but also trigger cell damage1-4, and both phenomena occur in hypoxia4-8. However, the precise mechanism by which acute hypoxia triggers mitochondrial ROS production is still unknown. Ca2+ is one of the best known examples of an ion acting as a second messenger9, yet the role ascribed to Na+ is to serve as a mere mediator of membrane potential and collaborating in ion transport10. Here we show that Na+ acts as a second messenger regulating OXPHOS function and ROS production by modulating fluidity of the inner mitochondrial membrane (IMM). We found that a conformational shift in mitochondrial complex I during acute hypoxia11 drives the acidification of the matrix and solubilization of calcium phosphate precipitates. The concomitant increase in matrix free-Ca2+ activates the mitochondrial Na+/Ca2+ exchanger (NCLX), which imports Na+ into the matrix. Na+ interacts with phospholipids reducing IMM fluidity and mobility of free ubiquinone between complex II and complex III, but not inside supercomplexes. As a consequence, superoxide is produced at complex III, generating a redox signal. Inhibition of mitochondrial Na+ import through NCLX is sufficient to block this pathway, preventing adaptation to hypoxia. These results reveal that Na+ import into the mitochondrial matrix controls OXPHOS function and redox signalling through an unexpected interaction with phospholipids, with profound consequences in cellular metabolism.

biochemistry↗