This study focuses on the interaction involved in the adhesion of mouse gametes and on the mechan... more This study focuses on the interaction involved in the adhesion of mouse gametes and on the mechanical properties of the oocyte membrane. The oocyte has an asymmetrical shape, and its membrane is composed of two distinct areas. One is rich in microvilli, and the other is smoother and without microvilli. With a biomembrane force probe (BFP) adapted to cell-cell measurements, we have quantified the separation forces between a spermatozoon and an oocyte. Microvillar and amicrovillar areas of the oocyte surface have been systematically probed and compared. In addition to a substantial difference in the elastic stiffness of these two regions, the experiments have revealed the presence of two types of membrane domains with different mechanical and adhesive properties, both distributed over the entire oocyte surface (i.e., in both microvillar and amicrovillar regions). If gamete contact occurs in the first type of domain, then the oocyte membrane deforms only elastically under traction. The pull-off forces in these domains are higher in the amicrovillar region. For a spermatozoon contact with the other type of domain, there can be a transition from the elastic to viscoelastic regime, and then tethers are extruded from the oocyte membrane.
European Biophysics Journal With Biophysics Letters, 1991
The interactions between unsaturated phospholipid bilayers deposited on mica were measured in aqu... more The interactions between unsaturated phospholipid bilayers deposited on mica were measured in aqueous solution using a surface forces apparatus. The bilayers were made of L-α-dioleoylphosphatidylcholine (DOPC), L-α-dioleoylphosphatidyl ethanolamine (DOPE), and mixtures of the two, and were formed on mica by Langmuir-Blodgett deposition after the lipids were spread on an aqueous substrate from a chloroform solution. The forces are interpreted as electrostatic double-layer and van der Waals forces with long range, and a strong repulsion (hydration or steric force) at distances of several nm. Together they produce a region of weak attraction (a secondary minimum) at 5 nm (DOPE) and 6 nm (DOPC). Fusion of two bilayers into one was observed when the local force per unit area was 2–3 MPa. Other researchers report that phosphatidylethanolamine in vesicles enhances fusion. In this study using deposited bilayers, the presence of DOPE in a DOPC bilayer did not promote fusion, nor did DOPE bilayers fuse more easily than DOPC. The value of the force per unit area at which the two bilayers fuse into one was however decreased by several orders of magnitude when the bilayers were formed from lipids kept in chloroform solution for several days or more. Chromatography showed traces of lipid degradation products in such chloroform solutions.
Carbohydate-carbohydrate recognition is emerging today as an important type of interaction in cel... more Carbohydate-carbohydrate recognition is emerging today as an important type of interaction in cell adhesion. One Ca2+mediated homotypic interaction between two LewisX determinants (LeX ) has been proposed to drive cell adhesion in murine embryogenesis. Here, the adhesion energies of lipid vesicles functionalised with glycolipids bearing monomeric or dimeric LeX determinants were measured in NaCl or CaCl2 media with the micropipette aspiration technique. These experiments on LeX with an environment akin to that provided by biological membrane confirmed the existence of this specific calcium dependant interaction of monomeric LeX . In contrast, dimeric LeX produced a repulsive contribution. By using a simple model involving the various contributions to the adhesion free energy, specific and non specific interactions could be separated and quantified. The involvement of calcium ions has been discussed in the monomeric and dimeric LeX lipids. Published in 2004.
To help understand the effects of protein adsorption on membrane filtration performance, we have ... more To help understand the effects of protein adsorption on membrane filtration performance, we have measured the molecular interactions between cellulose acetate films and two proteins with different properties (ribonuclease A and human serum albumin) with a surface force apparatus. Comparison of forces between two protein layers with those between a protein layer and a cellulose acetate (CA) film shows that,
The Surface Force Apparatus (SFA) measures directly, and with nanoscale resolution, the interacti... more The Surface Force Apparatus (SFA) measures directly, and with nanoscale resolution, the interaction energy vs. distance profile of planar arrays of biological molecules (e.g., lipids, polymers, or proteins). Through recent advances in the reconstitution and deposition of lipid bilayers, it is now possible to use SFA to study the interactions between membrane-incorporated biomolecules and to reveal any conformational changes and intermediate assembly states. Therein we describe two example systems. First, we show that using bilayers functionalized to carry DNA bases on their lipid headgroups, we can measure a macroscopic nucleoside–nucleoside adhesion force, from which one can obtain a molecular binding energy. Second, we describe the use of the SFA to study the interaction between SNARE proteins, which are involved in most of intracellular fusion events. Membrane fusion occurs when SNARE proteins assemble between lipid bilayers in the form of SNAREpins. SFA measurements between SNAREs embedded in lipid bilayers allowed us to elucidate the energetics and dynamics of SNAREpin folding, and to capture an intermediate binding state in SNAREpin assembly.
Carbohydate-carbohydrate recognition is emerging today as an important type of interaction in cel... more Carbohydate-carbohydrate recognition is emerging today as an important type of interaction in cell adhesion. One Ca2+mediated homotypic interaction between two LewisX determinants (LeX ) has been proposed to drive cell adhesion in murine embryogenesis. Here, the adhesion energies of lipid vesicles functionalised with glycolipids bearing monomeric or dimeric LeX determinants were measured in NaCl or CaCl2 media with the micropipette aspiration technique. These experiments on LeX with an environment akin to that provided by biological membrane confirmed the existence of this specific calcium dependant interaction of monomeric LeX . In contrast, dimeric LeX produced a repulsive contribution. By using a simple model involving the various contributions to the adhesion free energy, specific and non specific interactions could be separated and quantified. The involvement of calcium ions has been discussed in the monomeric and dimeric LeX lipids. Published in 2004.
Johnson-Kendall-Roberts (JKR) theory is an accurate model for strong adhesion energies of soft sl... more Johnson-Kendall-Roberts (JKR) theory is an accurate model for strong adhesion energies of soft slightly deformable material. Little is known about the validity of this theory on complex systems such as living cells. We have addressed this problem using a depletion controlled cell adhesion and measured the force necessary to separate the cells with a micropipette technique. We show that the cytoskeleton can provide the cells with a 3D structure that is sufficiently elastic and has a sufficiently low deformability for JKR theory to be valid. When the cytoskeleton is disrupted, JKR theory is no longer applicable.
The structure of DNA is the result of highly specific interactions between nucleotides (adenine a... more The structure of DNA is the result of highly specific interactions between nucleotides (adenine and thymine, cytosine and guanine) based on hydrogen bonds and size complementarities. We performed direct measurements of the forces between adenosine and thymidine using a surface force apparatus [J. Chem. Soc. Faraday I 74, 975-1001 (1978)]. These measurements showed that without the size effect hydrogen bonds
This study focuses on the interaction involved in the adhesion of mouse gametes and on the mechan... more This study focuses on the interaction involved in the adhesion of mouse gametes and on the mechanical properties of the oocyte membrane. The oocyte has an asymmetrical shape, and its membrane is composed of two distinct areas. One is rich in microvilli, and the other is smoother and without microvilli. With a biomembrane force probe (BFP) adapted to cell-cell measurements, we have quantified the separation forces between a spermatozoon and an oocyte. Microvillar and amicrovillar areas of the oocyte surface have been systematically probed and compared. In addition to a substantial difference in the elastic stiffness of these two regions, the experiments have revealed the presence of two types of membrane domains with different mechanical and adhesive properties, both distributed over the entire oocyte surface (i.e., in both microvillar and amicrovillar regions). If gamete contact occurs in the first type of domain, then the oocyte membrane deforms only elastically under traction. The pull-off forces in these domains are higher in the amicrovillar region. For a spermatozoon contact with the other type of domain, there can be a transition from the elastic to viscoelastic regime, and then tethers are extruded from the oocyte membrane.
European Biophysics Journal With Biophysics Letters, 1991
The interactions between unsaturated phospholipid bilayers deposited on mica were measured in aqu... more The interactions between unsaturated phospholipid bilayers deposited on mica were measured in aqueous solution using a surface forces apparatus. The bilayers were made of L-α-dioleoylphosphatidylcholine (DOPC), L-α-dioleoylphosphatidyl ethanolamine (DOPE), and mixtures of the two, and were formed on mica by Langmuir-Blodgett deposition after the lipids were spread on an aqueous substrate from a chloroform solution. The forces are interpreted as electrostatic double-layer and van der Waals forces with long range, and a strong repulsion (hydration or steric force) at distances of several nm. Together they produce a region of weak attraction (a secondary minimum) at 5 nm (DOPE) and 6 nm (DOPC). Fusion of two bilayers into one was observed when the local force per unit area was 2–3 MPa. Other researchers report that phosphatidylethanolamine in vesicles enhances fusion. In this study using deposited bilayers, the presence of DOPE in a DOPC bilayer did not promote fusion, nor did DOPE bilayers fuse more easily than DOPC. The value of the force per unit area at which the two bilayers fuse into one was however decreased by several orders of magnitude when the bilayers were formed from lipids kept in chloroform solution for several days or more. Chromatography showed traces of lipid degradation products in such chloroform solutions.
Carbohydate-carbohydrate recognition is emerging today as an important type of interaction in cel... more Carbohydate-carbohydrate recognition is emerging today as an important type of interaction in cell adhesion. One Ca2+mediated homotypic interaction between two LewisX determinants (LeX ) has been proposed to drive cell adhesion in murine embryogenesis. Here, the adhesion energies of lipid vesicles functionalised with glycolipids bearing monomeric or dimeric LeX determinants were measured in NaCl or CaCl2 media with the micropipette aspiration technique. These experiments on LeX with an environment akin to that provided by biological membrane confirmed the existence of this specific calcium dependant interaction of monomeric LeX . In contrast, dimeric LeX produced a repulsive contribution. By using a simple model involving the various contributions to the adhesion free energy, specific and non specific interactions could be separated and quantified. The involvement of calcium ions has been discussed in the monomeric and dimeric LeX lipids. Published in 2004.
To help understand the effects of protein adsorption on membrane filtration performance, we have ... more To help understand the effects of protein adsorption on membrane filtration performance, we have measured the molecular interactions between cellulose acetate films and two proteins with different properties (ribonuclease A and human serum albumin) with a surface force apparatus. Comparison of forces between two protein layers with those between a protein layer and a cellulose acetate (CA) film shows that,
The Surface Force Apparatus (SFA) measures directly, and with nanoscale resolution, the interacti... more The Surface Force Apparatus (SFA) measures directly, and with nanoscale resolution, the interaction energy vs. distance profile of planar arrays of biological molecules (e.g., lipids, polymers, or proteins). Through recent advances in the reconstitution and deposition of lipid bilayers, it is now possible to use SFA to study the interactions between membrane-incorporated biomolecules and to reveal any conformational changes and intermediate assembly states. Therein we describe two example systems. First, we show that using bilayers functionalized to carry DNA bases on their lipid headgroups, we can measure a macroscopic nucleoside–nucleoside adhesion force, from which one can obtain a molecular binding energy. Second, we describe the use of the SFA to study the interaction between SNARE proteins, which are involved in most of intracellular fusion events. Membrane fusion occurs when SNARE proteins assemble between lipid bilayers in the form of SNAREpins. SFA measurements between SNAREs embedded in lipid bilayers allowed us to elucidate the energetics and dynamics of SNAREpin folding, and to capture an intermediate binding state in SNAREpin assembly.
Carbohydate-carbohydrate recognition is emerging today as an important type of interaction in cel... more Carbohydate-carbohydrate recognition is emerging today as an important type of interaction in cell adhesion. One Ca2+mediated homotypic interaction between two LewisX determinants (LeX ) has been proposed to drive cell adhesion in murine embryogenesis. Here, the adhesion energies of lipid vesicles functionalised with glycolipids bearing monomeric or dimeric LeX determinants were measured in NaCl or CaCl2 media with the micropipette aspiration technique. These experiments on LeX with an environment akin to that provided by biological membrane confirmed the existence of this specific calcium dependant interaction of monomeric LeX . In contrast, dimeric LeX produced a repulsive contribution. By using a simple model involving the various contributions to the adhesion free energy, specific and non specific interactions could be separated and quantified. The involvement of calcium ions has been discussed in the monomeric and dimeric LeX lipids. Published in 2004.
Johnson-Kendall-Roberts (JKR) theory is an accurate model for strong adhesion energies of soft sl... more Johnson-Kendall-Roberts (JKR) theory is an accurate model for strong adhesion energies of soft slightly deformable material. Little is known about the validity of this theory on complex systems such as living cells. We have addressed this problem using a depletion controlled cell adhesion and measured the force necessary to separate the cells with a micropipette technique. We show that the cytoskeleton can provide the cells with a 3D structure that is sufficiently elastic and has a sufficiently low deformability for JKR theory to be valid. When the cytoskeleton is disrupted, JKR theory is no longer applicable.
The structure of DNA is the result of highly specific interactions between nucleotides (adenine a... more The structure of DNA is the result of highly specific interactions between nucleotides (adenine and thymine, cytosine and guanine) based on hydrogen bonds and size complementarities. We performed direct measurements of the forces between adenosine and thymidine using a surface force apparatus [J. Chem. Soc. Faraday I 74, 975-1001 (1978)]. These measurements showed that without the size effect hydrogen bonds
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Papers by Eric Perez