Mauro Dalla Serra is a Senior Research Scientist of the National Research Council of Italy and Head of the Unit at Trento of the Institute of Biophysics. His scientific research interest is to investigate the structural and functional aspects of the interaction of membrane-active molecules with natural and model lipid membranes. A large portion of his work has been dedicated to protein-protein and protein-lipid interaction, to understand the mechanism of action of pore-forming proteins, that are relevant for human health. He has published more than 90 peer reviewed articles and contributed 17 chapters to multi-authored books.
Pore formation of cellular membranes is an ancient mechanism of bacterial pathogenesis that allow... more Pore formation of cellular membranes is an ancient mechanism of bacterial pathogenesis that allows efficient damaging of target cells. Several mechanisms have been described, however, relatively little is known about the assembly and properties of pores. Listeriolysin O (LLO) is a pH-regulated cholesterol-dependent cytolysin from the intracellular pathogen Listeria monocytogenes, which forms transmembrane β-barrel pores. Here we report that the assembly of LLO pores is rapid and efficient irrespective of pH. While pore diameters at the membrane surface are comparable at either pH 5.5 or 7.4, the distribution of pore conductances is significantly pH-dependent. This is directed by the unique residue H311, which is also important for the conformational stability of the LLO monomer and the rate of pore formation. The functional pores exhibit variations in height profiles and can reconfigure significantly by merging to other full pores or arcs. Our results indicate significant plasticity...
Pore-forming toxins are an important group of natural molecules that damage cellular membranes by... more Pore-forming toxins are an important group of natural molecules that damage cellular membranes by forming transmembrane pores. They are used by many organisms for attack or defense and similar proteins are employed in the immune system of vertebrates. Various biophysical approaches have been used to understand how these proteins act at the molecular level. One of the most useful, in terms of monitoring pore formation in real time, is a method that employs planar lipid membranes and involves ionic current measurements. Here we highlight the advantages and possibilities that this approach offers and show how it can advance understanding of the pore-forming mechanism and pore properties for one of the most important families of natural toxins, the cholesterol-dependent cytolysins.
Pore-forming toxins are an important group of natural molecules that damage cellular membranes by... more Pore-forming toxins are an important group of natural molecules that damage cellular membranes by forming transmembrane pores. They are used by many organisms for attack or defense and similar proteins are employed in the immune system of vertebrates. Various biophysical approaches have been used to understand how these proteins act at the molecular level. One of the most useful, in terms of monitoring pore formation in real time, is a method that employs planar lipid membranes and involves ionic current measurements. Here we highlight the advantages and possibilities that this approach offers and show how it can advance understanding of the pore-forming mechanism and pore properties for one of the most important families of natural toxins, the cholesterol-dependent cytolysins.
Sarcolemmal membrane vesicles isolated from bovine ventricular tissue accumulate Ca2+ through the... more Sarcolemmal membrane vesicles isolated from bovine ventricular tissue accumulate Ca2+ through the Na+/Ca2+ exchanger when exposed to an outwardly directed Na+ gradient. This Ca2+ is then released by the same mechanism if the vesicles are transferred to a Ca(2+)-depleted Na+ buffer. Using the Ca+ indicator, arsenazo III, and a stopped-flow spectrophotometer, we can directly follow the kinetics of Ca2+ extrusion. We can thus measure the activity of the Na+/Ca2+ exchanger by the initial rate of Ca2+ release. We found that it depends upon the external Na+ concentration in a cooperative way, with a Hill coefficient of 2. By studying the temperature dependence of Na+/Ca2+ exchange, we found that it can be described by a single activation energy: Ea = 8.3 +/- 0.4 Kcal/mol. When the Na+/Ca2+ exchanger is reconstituted into lipid vesicles of defined composition, we observe a higher activity if cholesterol is among the lipids. The activation energy becomes 6.1 +/- 0.1 Kcal/mol in this system,...
The interfacing of artificial devices with biological systems is a challenging field that crosses... more The interfacing of artificial devices with biological systems is a challenging field that crosses several disciplines ranging from fundamental research (biophysical chemistry, neurobiology, material and surface science) to frontier technological application (nanotechnology, bioelectronics). The memristor is the fourth fundamental circuit element, whose electrical properties favor applications in signal processing, neural networks, and brain-computer interactions and it represents a new frontier for technological applications in many fields including the nanotechnologies, bioelectronics and the biosensors. Using multidisciplinary approaches, covering surface science, cell biology and electrophysiology, we successfully implemented a living bio-hybrid system constituted by cells adhering to films of poly(aniline) (PANI), a semiconductor polymer having memristive properties assembled with polyelectrolytes. Here we tested whether the PANI devices could support survivor, adhesion and differentiation of several cell lines, including the neuron-like SHSY5Y cells. Moreover, we performed electrophysiology on these cells showing that the biophysical properties are retained with differences occurring in the recorded ion currents. Taken together, the cell viability here reported is the key requirement to design and develop a reliable functional memristor-based bio-hybrid able to mimic neuronal activity and plasticity.
Listeriolysin O (LLO) is the major factor implicated in the escape of Listeria monocytogenes from... more Listeriolysin O (LLO) is the major factor implicated in the escape of Listeria monocytogenes from the phagolysosome. It is the only representative of cholesterol-dependent cytolysins that exhibits pH-dependent activity. Despite intense studies of LLO pH-dependence, this feature of the toxin still remains incompletely explained. Here we used fluorescence and CD spectroscopy to show that the structure of LLO is not detectably affected by pH at room temperature. We observed slightly altered haemolytic and permeabilizing activities at different pH values, which we relate to reduced binding of LLO to the lipid membranes. However, alkaline pH and elevated temperatures caused rapid denaturation of LLO. Aggregates of the toxin were able to bind Congo red and Thioflavin T dyes and were visible under transmission electron microscopy as large, amorphous, micrometer-sized assemblies. The aggregates had the biophysical properties of amyloid. Analytical ultracentrifugation indicated dimerization of the protein in acidic conditions, which protects the protein against premature denaturation in the phagolysosome, where toxin activity takes place. We therefore suggest that LLO spontaneously aggregates at the neutral pH found in the host cell cytosol and that this is a major mechanism of LLO inactivation.
Pore formation of cellular membranes is an ancient mechanism of bacterial pathogenesis that allow... more Pore formation of cellular membranes is an ancient mechanism of bacterial pathogenesis that allows efficient damaging of target cells. Several mechanisms have been described, however, relatively little is known about the assembly and properties of pores. Listeriolysin O (LLO) is a pH-regulated cholesterol-dependent cytolysin from the intracellular pathogen Listeria monocytogenes, which forms transmembrane β-barrel pores. Here we report that the assembly of LLO pores is rapid and efficient irrespective of pH. While pore diameters at the membrane surface are comparable at either pH 5.5 or 7.4, the distribution of pore conductances is significantly pH-dependent. This is directed by the unique residue H311, which is also important for the conformational stability of the LLO monomer and the rate of pore formation. The functional pores exhibit variations in height profiles and can reconfigure significantly by merging to other full pores or arcs. Our results indicate significant plasticity of large β-barrel pores, controlled by environmental cues like pH.
Pore formation of cellular membranes is an ancient mechanism of bacterial pathogenesis that allow... more Pore formation of cellular membranes is an ancient mechanism of bacterial pathogenesis that allows efficient damaging of target cells. Several mechanisms have been described, however, relatively little is known about the assembly and properties of pores. Listeriolysin O (LLO) is a pH-regulated cholesterol-dependent cytolysin from the intracellular pathogen Listeria monocytogenes, which forms transmembrane β-barrel pores. Here we report that the assembly of LLO pores is rapid and efficient irrespective of pH. While pore diameters at the membrane surface are comparable at either pH 5.5 or 7.4, the distribution of pore conductances is significantly pH-dependent. This is directed by the unique residue H311, which is also important for the conformational stability of the LLO monomer and the rate of pore formation. The functional pores exhibit variations in height profiles and can reconfigure significantly by merging to other full pores or arcs. Our results indicate significant plasticity...
Pore-forming toxins are an important group of natural molecules that damage cellular membranes by... more Pore-forming toxins are an important group of natural molecules that damage cellular membranes by forming transmembrane pores. They are used by many organisms for attack or defense and similar proteins are employed in the immune system of vertebrates. Various biophysical approaches have been used to understand how these proteins act at the molecular level. One of the most useful, in terms of monitoring pore formation in real time, is a method that employs planar lipid membranes and involves ionic current measurements. Here we highlight the advantages and possibilities that this approach offers and show how it can advance understanding of the pore-forming mechanism and pore properties for one of the most important families of natural toxins, the cholesterol-dependent cytolysins.
Pore-forming toxins are an important group of natural molecules that damage cellular membranes by... more Pore-forming toxins are an important group of natural molecules that damage cellular membranes by forming transmembrane pores. They are used by many organisms for attack or defense and similar proteins are employed in the immune system of vertebrates. Various biophysical approaches have been used to understand how these proteins act at the molecular level. One of the most useful, in terms of monitoring pore formation in real time, is a method that employs planar lipid membranes and involves ionic current measurements. Here we highlight the advantages and possibilities that this approach offers and show how it can advance understanding of the pore-forming mechanism and pore properties for one of the most important families of natural toxins, the cholesterol-dependent cytolysins.
Sarcolemmal membrane vesicles isolated from bovine ventricular tissue accumulate Ca2+ through the... more Sarcolemmal membrane vesicles isolated from bovine ventricular tissue accumulate Ca2+ through the Na+/Ca2+ exchanger when exposed to an outwardly directed Na+ gradient. This Ca2+ is then released by the same mechanism if the vesicles are transferred to a Ca(2+)-depleted Na+ buffer. Using the Ca+ indicator, arsenazo III, and a stopped-flow spectrophotometer, we can directly follow the kinetics of Ca2+ extrusion. We can thus measure the activity of the Na+/Ca2+ exchanger by the initial rate of Ca2+ release. We found that it depends upon the external Na+ concentration in a cooperative way, with a Hill coefficient of 2. By studying the temperature dependence of Na+/Ca2+ exchange, we found that it can be described by a single activation energy: Ea = 8.3 +/- 0.4 Kcal/mol. When the Na+/Ca2+ exchanger is reconstituted into lipid vesicles of defined composition, we observe a higher activity if cholesterol is among the lipids. The activation energy becomes 6.1 +/- 0.1 Kcal/mol in this system,...
The interfacing of artificial devices with biological systems is a challenging field that crosses... more The interfacing of artificial devices with biological systems is a challenging field that crosses several disciplines ranging from fundamental research (biophysical chemistry, neurobiology, material and surface science) to frontier technological application (nanotechnology, bioelectronics). The memristor is the fourth fundamental circuit element, whose electrical properties favor applications in signal processing, neural networks, and brain-computer interactions and it represents a new frontier for technological applications in many fields including the nanotechnologies, bioelectronics and the biosensors. Using multidisciplinary approaches, covering surface science, cell biology and electrophysiology, we successfully implemented a living bio-hybrid system constituted by cells adhering to films of poly(aniline) (PANI), a semiconductor polymer having memristive properties assembled with polyelectrolytes. Here we tested whether the PANI devices could support survivor, adhesion and differentiation of several cell lines, including the neuron-like SHSY5Y cells. Moreover, we performed electrophysiology on these cells showing that the biophysical properties are retained with differences occurring in the recorded ion currents. Taken together, the cell viability here reported is the key requirement to design and develop a reliable functional memristor-based bio-hybrid able to mimic neuronal activity and plasticity.
Listeriolysin O (LLO) is the major factor implicated in the escape of Listeria monocytogenes from... more Listeriolysin O (LLO) is the major factor implicated in the escape of Listeria monocytogenes from the phagolysosome. It is the only representative of cholesterol-dependent cytolysins that exhibits pH-dependent activity. Despite intense studies of LLO pH-dependence, this feature of the toxin still remains incompletely explained. Here we used fluorescence and CD spectroscopy to show that the structure of LLO is not detectably affected by pH at room temperature. We observed slightly altered haemolytic and permeabilizing activities at different pH values, which we relate to reduced binding of LLO to the lipid membranes. However, alkaline pH and elevated temperatures caused rapid denaturation of LLO. Aggregates of the toxin were able to bind Congo red and Thioflavin T dyes and were visible under transmission electron microscopy as large, amorphous, micrometer-sized assemblies. The aggregates had the biophysical properties of amyloid. Analytical ultracentrifugation indicated dimerization of the protein in acidic conditions, which protects the protein against premature denaturation in the phagolysosome, where toxin activity takes place. We therefore suggest that LLO spontaneously aggregates at the neutral pH found in the host cell cytosol and that this is a major mechanism of LLO inactivation.
Pore formation of cellular membranes is an ancient mechanism of bacterial pathogenesis that allow... more Pore formation of cellular membranes is an ancient mechanism of bacterial pathogenesis that allows efficient damaging of target cells. Several mechanisms have been described, however, relatively little is known about the assembly and properties of pores. Listeriolysin O (LLO) is a pH-regulated cholesterol-dependent cytolysin from the intracellular pathogen Listeria monocytogenes, which forms transmembrane β-barrel pores. Here we report that the assembly of LLO pores is rapid and efficient irrespective of pH. While pore diameters at the membrane surface are comparable at either pH 5.5 or 7.4, the distribution of pore conductances is significantly pH-dependent. This is directed by the unique residue H311, which is also important for the conformational stability of the LLO monomer and the rate of pore formation. The functional pores exhibit variations in height profiles and can reconfigure significantly by merging to other full pores or arcs. Our results indicate significant plasticity of large β-barrel pores, controlled by environmental cues like pH.
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Papers by Mauro Dalla Serra