Seven days of gamma-hydroxybutyrate (GHB) use produces severe withdrawal.
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Adult↗
Biomedical subjects
Eric Perez
Publications and source records attributed to Eric Perez.
Structure, surface interactions, and compressibility of bacterial S-layers through scanning force microscopy and the surface force apparatus.
Two-dimensional crystalline bacterial surface layers (S-layers) are found in a broad range of bacteria and archaea as the outermost cell envelope component. The self-assembling properties of the S-layers permit them to recrystallize on solid substrates. Beyond their biological interest as S-layers, they are currently used in nanotechnology to build supramolecular structures. Here, the structure of S-layers and the interactions between them are studied through surface force techniques. Scanning force microscopy has been used to study the structure of recrystallized S-layers from Bacillus sphaericus on mica at different 1:1 electrolyte concentrations. They give evidence of the two-dimensional organization of the proteins and reveal small corrugations of the S-layers formed on mica. The lattice parameters of the S-layers were a=b=14 nm, gamma=90 degrees and did not depend on the electrolyte concentration. The interaction forces between recrystallized S-layers on mica were studied with the surface force apparatus as a function of electrolyte concentration. Force measurements show that electrostatic and steric interactions are dominant at long distances. When the S-layers are compressed they exhibit elastic behavior. No adhesion between recrystallized layers takes place. We report for the first time, to our knowledge, the value of the compressibility modulus of the S-layer (0.6 MPa). The compressibility modulus is independent on the electrolyte concentration, although loads of 20 mN m-1 damage the layer locally. Control experiments with denatured S-proteins show similar elastic properties under compression but they exhibit adhesion forces between proteins, which were not observed in recrystallized S-layers.
Bacterial Proteins↗
Spontaneous and reversible switch from amphiphilic to oil-like structures.
Current theories assume that the amphiphilicity of biological membranes is always preserved. We observed that two hydrogen-bonding lipid layers in contact can spontaneously and reversibly lose their amphiphilic structure and turn into an assembly of oily complexes. This result opens a new angle for understanding the reorganization of lipids during membrane fusion, since similar complexes could fill the troubling hydrophobic voids displayed in the current models. The unique tribological properties described here may also find application in the development of novel nanolubricants.
Hydrogen Bonding↗
Prototypical type I E-cadherin and type II cadherin-7 mediate very distinct adhesiveness through their extracellular domains.
Using a dual pipette assay that measures the force required to separate adherent cell doublets, we have quantitatively compared intercellular adhesiveness mediated by Type I (E- or N-cadherin) or Type II (cadherin-7 or -11) cadherins. At similar cadherin expression levels, cells expressing Type I cadherins adhered much more rapidly and strongly than cells expressing Type II cadherins. Using chimeric cadherins, we found that the extracellular domain exerts by far the dominant effect on cell adhesivity, that of E-cadherin conferring high adhesivity, and that of cadherin-7 conferring low adhesivity. Type I cadherins were incorporated to a greater extent into detergent-insoluble cytoskeletal complexes, and their cytoplasmic tails were much more effective in disrupting strong adherent junctions, suggesting that Type II cadherins form less stable complexes with beta-catenin. The present study demonstrates compellingly, for the first time, that cadherins are dramatically different in their ability to promote intercellular adhesiveness, a finding that has profound implications for the regulation of tissue morphogenesis.
Animals↗
The binding energy of two nitrilotriacetate groups sharing a nickel ion.
Among the various molecular interactions used to construct supramolecular self-assembling systems, homoliganded metallic NTA-Ni-NTA complexes have received little attention despite their considerable potential applications, such as the connection of different biochemical functions. The stability of this complex is investigated here by using two concordant nanotechniques (surface forces apparatus and vesicle micromanipulation) that allow direct measurements of adhesion energies due to the chelation of nickel ions by nitrilotriacetate (NTA) groups grafted on surfaces. We show that two NTA groups can share a nickel ion, and that the association of a Ni-NTA complex with an NTA group has a molecular binding energy of 1.4 kcal/mol. Binding measurements in bulk by isothermal titration calorimetry experiments give the same value and, furthermore, indicate that the Ni-NTA chelation bond is about five times stronger than the NTA-Ni-NTA one. This first direct proof and quantification of the simultaneous chelation of a nickel ion by two NTA groups sheds new light on association dynamics involving chelation processes and offers perspectives for the development of new supramolecular assemblies and anchoring strategies.
Journal Article↗
The natural LewisX-bearing lipids promote membrane adhesion: influence of ceramide on carbohydrate-carbohydrate recognition.
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Carbohydrate Sequence↗
Johnson-Kendall-Roberts theory applied to living cells.
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.
Animals↗
Force measurements in E-cadherin-mediated cell doublets reveal rapid adhesion strengthened by actin cytoskeleton remodeling through Rac and Cdc42.
We have used a modified, dual pipette assay to quantify the strength of cadherin-dependent cell-cell adhesion. The force required to separate E-cadherin-expressing paired cells in suspension was measured as an index of intercellular adhesion. Separation force depended on the homophilic interaction of functional cadherins at the cell surface, increasing with the duration of contact and with cadherin levels. Severing the link between cadherin and the actin cytoskeleton or disrupting actin polymerization did not affect initiation of cadherin-mediated adhesion, but prevented it from developing and becoming stronger over time. Rac and Cdc42, the Rho-like small GTPases, were activated when E-cadherin-expressing cells formed aggregates in suspension. Overproduction of the dominant negative form of Rac or Cdc42 permitted initial E-cadherin-based adhesion but affected its later development; the dominant active forms prevented cell adhesion outright. Our findings highlight the crucial roles played by Rac, Cdc42, and actin cytoskeleton dynamics in the development and regulation of strong cell adhesion, defined in terms of mechanical forces.
Actins↗
Separation force measurements reveal different types of modulation of E-cadherin-based adhesion by nectin-1 and -3.
Nectins are Ca2+-independent cell adhesion molecules found at cadherin-based adherens junctions. We used a dual pipette assay that measures the forces required to separate cell doublets to determine how nectins affect the formation and strength of cell-cell adhesion. Less force was required to separate doublets of L cells expressing nectin-1 or nectin-3 than to separate doublets of E-cadherin-expressing cells. Heterodimers formed between cells expressing nectin-1 or nectin-3 adhered more strongly than homodimers. Nectin-3 that does not trans-interact with nectin-1 inhibited E-cadherin-mediated adhesion. However, the extracellular fragment of nectin-1 did not have an agonistic effect on E-cadherin-dependent cell adhesion when it trans-interacted with nectin-3, expressed at high levels in cells. In contrast, the extracellular fragment of nectin-3 had a significant agonistic effect on cadherin-based adhesion when it interacted with endogenous nectin-1, expressed at low levels in cells. Our results indicate that E-cadherin is the key molecule involved in cell adhesion and that the regulation of E-cadherin-based adhesion involving cellular nectin-1 trans-interacting with nectin-3 is qualitatively different from that involving cellular nectin-3 trans-interacting with nectin-1 and depends on the nectin levels expressed by cells.
Animals↗
Specific and non specific interactions involving Le( X ) determinant quantified by lipid vesicle micromanipulation.
Carbohydrate-carbohydrate recognition is emerging today as an important type of interaction in cell adhesion. One Ca(2+)mediated homotypic interaction between two Lewis( X ) determinants (Le( X )) has been proposed to drive cell adhesion in murine embryogenesis. Here, the adhesion energies of lipid vesicles functionalized with glycolipids bearing monomeric or dimeric Le( X ) determinants were measured in NaCl or CaCl(2) media with the micropipette aspiration technique. These experiments on Le( X ) with an environment akin to that provided by biological membrane confirmed the existence of this specific calcium dependent interaction of monomeric Le( X ). In contrast, dimeric Le( X ) 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 Le( X ) lipids.
Calcium↗
Nanocapsules with functionalized surfaces and walls.
With the possibility of creating and handling nanometer-sized objects, it became popular to dream of future miniaturized tools allowing completely new applications in medicine and technology. Mother nature created during evolution many such self-assembled highly sophisticated and robust objects, and it is very tempting to modify them for other purposes: artificial cells as intelligent submarines floating in the bloodstream attacking cancer cells, single-molecule detection and manipulation allowing the bottom-up construction of devices, and so on. Nanobiotechnology became a hot topic and significant budgets have been attributed to it. However, caution has to be paid that unrealistic dreams might have a fairly negative effect on the taxpayer seeing unkept promises. In this paper, we explore the possibilities of using biological substances in material science.
Biocompatible Materials↗
Dose-dependent hemodynamic effect of digoxin therapy in severe verapamil toxicity.
UNLABELLED: Calcium chloride (CaCl(2)) alone is an ineffective antidote in severe calcium channel antagonist overdoses. Digoxin has been evaluated as a therapy to increase the effectiveness of calcium in severe calcium channel antagonist overdoses. OBJECTIVE: To determine if there is a dose-dependent hemodynamic effect of digoxin in the setting of severe verapamil toxicity treated with high-dose CaCl(2). METHODS: Eight dogs were instrumented to measure systolic and diastolic blood pressure, cardiac output, pulmonary artery pressures, and left ventricular pressures. Verapamil toxicity (50% decrease in mean arterial pressure) was induced with verapamil 6 mg/kg/hr and maintained for 30 minutes by titrating the verapamil rate. Following verapamil toxicity, each dog received one dose of digoxin equivalent to 0, 1, 1.5, 2, 3, 4, 6, or 8 times the loading dose of digoxin (0.009 mg/kg). The verapamil rate was changed to 4 mg/kg/hr and continued for the next five hours. CaCl(2) boluses were given (0.5 g immediately following verapamil toxicity and 1 g at one, two, and three hours). Measurements were compared with the loading dose of digoxin using linear regression analysis. RESULTS: Digoxin resulted in a dose-dependent increase in systolic blood pressure at 4 hours (10.23 mm Hg/loading dose of digoxin, 95% CI = 2.74 to 17.73), 4 hours, 15 minutes (13.9 mm Hg/loading dose of digoxin, 95% CI = 8.75 to 19.01), and 5 hours (17.04 mm Hg/loading dose of digoxin, 95% CI = 1.76 to 32.32). Digoxin resulted in a dose-dependent increase in maximal ventricular pressure at the end of hour 3 (8.55 mm Hg/loading dose of digoxin, 95% CI = 3.41 to 13.69), 3 hours, 15 minutes (11.81 mm Hg/loading dose of digoxin, 95% CI = 4.89 to 18.73), hour 4 (8.26 mm Hg/loading dose of digoxin, 95% CI = 1.03 to 15.48), and 4 hours, 15 minutes (9.74 mm Hg/loading dose of digoxin, 95% CI = 4.47 to 15.00). The authors were unable to detect a dose-dependent increase in other parameters, including diastolic relaxation (diastolic change in pressure over time) and time to onset of death. No ventricular arrhythmias developed in any dogs. CONCLUSIONS: There is a dose-dependent effect of digoxin on systolic blood pressure and maximal ventricular pressure in the setting of severe verapamil toxicity treated with high-dose CaCl(2).
Animals↗
Energy of hydrogen bonds probed by the adhesion of functionalized lipid layers.
It is now well admitted that hydrophobic interactions and hydrogen bonds are the main forces driving protein folding and stability. However, because of the complex structure of a protein, it is still difficult to separate the different energetic contributions and have a reliable estimate of the hydrogen bond part. This energy can be quantified on simpler systems such as surfaces bearing hydrogen-bonding groups. Using the surface force apparatus, we have directly measured the interaction energy between monolayers of lipids whose headgroups can establish hydrogen bonds in water: nitrilotriacetate, adenosine, thymidine, and methylated thymidine lipids. From the adhesion energy between the surfaces, we have deduced the energy of a single hydrogen bond in water. We found in each case an energy of 0.5 kcal/mol. This result is in good agreement with recent experimental and theoretical studies made on protein systems showing that intramolecular hydrogen bonds make a positive contribution to protein stabilization.
Energy Transfer↗