Navegando por Autor "Carvalho, Antônio F."

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Binding of folic acid induces specific self-aggregation of lactoferrin: thermodynamic characterization
(Langmuir, 2015-10-21) Tavares, Guilherme M.; Croguennec, Thomas; Le, Sébastien; Lerideau, Olivia; Hamon, Pascaline; Carvalho, Antônio F.; Bouhallab, Saïd
In the study presented here, we investigated the interaction at pH 5.5 between folic acid (FA) and lactoferrin (LF), a positively charged protein. We found a binding constant Ka of 10(5) M(-1) and a high stoichiometry of 10 mol of FA/mol of LF. The size and charge of the complexes formed evolved during titration experiments. Increasing the ionic strength to 50 mM completely abolished the isothermal titration calorimetry (ITC) signal, suggesting the predominance of electrostatic interactions in the exothermic binding obtained. We developed a theoretical model that explains the complex triphasic ITC profile. Our results revealed a two-step mechanism: FA/LF interaction followed by self-association of the complexes thus formed. We suggest that 10 FA molecules bind to LF to form saturated reactive complexes (FA10/LF) that further self-associate into aggregates with a finite size of around 15 nm. There is thus a critical saturation degree of the protein, above which the self-association can take place. We present here the first results that provide comprehensive details of the thermodynamics of FA/LF complexation-association. Given the high stoichiometry, allowing a load of 55 mg of FA/g of LF, we suggest that FA/LF aggregates would be an effective vehicle for FA in fortified drinks.
Enumeration of starter cultures during yogurt production using Petrifilm™ AC plates associated with acidified MRS and M17 broths
(Journal of Dairy Research, 2009-03-13) Gonçalves, Marília M.; Freitas, Rosangela; Nero, Luís A.; Carvalho, Antônio F.
The efficiency of Petrifilm TM AC (3M Microbiology, St. Paul, MN, USA) associated with the broths M17 and de Mann-Rogosa-Sharpe (MRS) at pH 5.4 was evaluated to enumerate Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus during the yogurt production. Commercial and reference strains of these microorganisms were experimentally inoculated in nonfat milk and incubated at 42 8C for 4 h for yogurt production. At the moment of inoculation and after incubation, aliquots were collected, submitted to dilution using the broths M17 and MRS at pH 5.4, and plated for Strep. salivarius and Lb. bulgaricus enumeration according ISO 9232 and at Petrifilm TM AC plates, respectively. M17 plates were incubated at 42 8C, and MRS plates were incubated at 35 8C under anaerobiosis. After 48 h, the formed colonies were enumerated and the counts were compared by correlation and analysis of variance (P < 0.05). In addition, colonies were randomly selected from all plates and characterized according to Gram staining and morphology. The obtained results indicated that Petrifilm TM AC plates associated to M17 and MRS at pH 5.4 can be considered as a suitable alternative for Strep. salivarius and Lb. bulgaricus enumeration during yogurt production, with slight interferences due to the acidity of MRS at the moment of inoculation, and due to the acidity of yogurt at the end of fermentation process. It was also observed that the MRS at pH 5.4 was not sufficiently selective for Lb. delbrueckii enumeration, despite it is indicated by the official protocol from ISO 9232.
How the presence of a small molecule affects the complex coacervation between lactoferrin and β-lactoglobulin
(International Journal of Biological Macromolecules, 2017-09) Tavares, Guilherme M.; Croguennec, Thomas; Hamon, Pascaline; Carvalho, Antônio F.; Saïd Bouhallab
Heteroprotein complex coacervation corresponds to the formation of two liquid phases in equilibrium induced by the interaction of two oppositely charged proteins. The more concentrated phase known as coacervate phase, has attracted interest from several fields of science due to its potential applications for example for encapsulation and delivery of bioactives. Prior such application, it is necessary to understand how the presence of small ligands affects the complex coacervation. In this work, we report on the interaction of small ligand with individual proteins β-lactoglobulin (β-LG) and lactoferrin (LF) and consequences on their complex coacervation. ANS (8-Anilinonaphthalene-1-sulfonic acid), a fluorescent probe, was used as model ligand. While ANS did not interact with β-LG, it presented two sets of binding sites with LF inducing its self-aggregation. Depending on its concentration, ANS modulated the shape of β-LG-LF macromolecular assembly. Coacervates were observed for ANS/LF molar ratio <25 against amorphous aggregates for higher ANS/LF molar ratios. A maximum loading capacity of around 40 mg of ANS per gram of LF in the formed heteroprotein coacervates was reached.
How the presence of a small molecule affects the complex coacervation between lactoferrin and ␤-lactoglobulin
(International Journal of Biological Macromolecules, 2017-04-04) Tavares, Guilherme Miranda; Carvalho, Antônio F.; Croguennec, Thomas; Hamon, Pascaline; Bouhallab, Saïd
Heteroprotein complex coacervation corresponds to the formation of two liquid phases in equilibrium induced by the interaction of two oppositely charged proteins. The more concentrated phase known as coacervate phase, has attracted interest from several fields of science due to its potential applications for example for encapsulation and delivery of bioactives. Prior such application, it is necessary to understand how the presence of small ligands affects the complex coacervation. In this work, we report on the interaction of small ligand with individual proteins β-lactoglobulin (β-LG) and lactoferrin (LF) and consequences on their complex coacervation. ANS (8-Anilinonaphthalene-1-sulfonic acid), a fluorescent probe, was used as model ligand. While ANS did not interact with β-LG, it presented two sets of binding sites with LF inducing its self-aggregation. Depending on its concentration, ANS modulated the shape of β-LG-LF macromolecular assembly. Coacervates were observed for ANS/LF molar ratio <25 against amorphous aggregates for higher ANS/LF molar ratios. A maximum loading capacity of around 40 mg of ANS per gram of LF in the formed heteroprotein coacervates was reached.
Selective coacervation between lactoferrin and the two isoforms of β-lactoglobulin
(Food Hydrocolloids, 2015-06) Tavares, Guilherme M.; Croguennec, Thomas; Hamon, Pascaline; Carvalho, Antônio F.; Bouhallab, Saïd
This work reports on the impact of subtle change of protein charge on coacervation and subsequent liquid–liquid phase separation between two oppositely charged globular proteins. For this purpose, a comparative study was conducted on the coacervation of lactoferrin (LF) with the two β-lactoglobulin (β-LG) isoforms. Upon mixing LF with an excess of β-LG, microspheres were formed throughout coacervation under narrow pH range (5.4–6.0). At the optimal pH of coacervation, LF being the limiting partner under tested concentration ranges. The β-LG/LF molar ratio recovered in the formed coacervates varied from 4 to 8 depending on the total protein concentration. Remarkably, LF showed a selective coacervation with isoform A of β-LG as judged by a larger concentration domain for coacervation and a high yield of LF recovered once mixed with β-LG A i.e. 80% against a maximum of 42% with β-LG B. At thermodynamic level, the interaction of LF with both β-LG isoforms exhibited complex exothermic binding isotherms with both enthalpic and entropic contributions.