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A molecular mechanism for modulating plasma Zn speciation by fatty acids.

Lu J, Stewart AJ, Sleep D, Sadler PJ, Pinheiro TJ, Blindauer CA - J. Am. Chem. Soc. (2012)

Bottom Line: Albumin transports both fatty acids and zinc in plasma.The molecular mechanism for this effect is likely due to a large conformational change elicited by fatty acid binding to a high-affinity interdomain site that disrupts at least one Zn site.Albumin may be a molecular device to "translate" certain aspects of the organismal energy state into global zinc signals.

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Affiliation: Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK.

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Competitive binding ofmetals and MYR to BSA. (A) Effect of increasingamounts of MYR on the zinc-binding capacity of BSA. ITC curves fortitrations of 333 μM Zn2+ into 25 μM BSA inthe presence and absence of varying amounts (0–5 molar equiv)of MYR in 50 mM Tris/50 mM NaCl (pH 7.2). The fits (Figure S8) allowed estimates of the ratio of site A availability,as shown in (B). A clear downward trend was observed. A 4:1 MYR:Znmolar ratio suppressed occupation of site A almost completely. A secondbinding site was also affected by fatty acid binding (see D). (C)ITC curves for titrations of 500 μM MYR into 12.5 μM BSAor Zn1BSA. These titrations were carried out in H2O because of the insufficient solubility of MYR in Tris buffer. Thefits (Figure S9) correspond to a modelwith one set of binding sites to estimate the stoichiometry for thehighest-affinity sites. This equaled 5.0 ± 0.3, and the averagelog K was 6.3 ± 0.4 in the absence and 5.9 ±0.4 in the presence of Zn2+. More complex fits were possible,but the data were insufficient to justify them. (D) 111Cd NMR spectra of Cd2BSA recorded in the absence and presenceof 5 molar equiv of MYR. Peaks A and B were both suppressed by MYR.
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fig5: Competitive binding ofmetals and MYR to BSA. (A) Effect of increasingamounts of MYR on the zinc-binding capacity of BSA. ITC curves fortitrations of 333 μM Zn2+ into 25 μM BSA inthe presence and absence of varying amounts (0–5 molar equiv)of MYR in 50 mM Tris/50 mM NaCl (pH 7.2). The fits (Figure S8) allowed estimates of the ratio of site A availability,as shown in (B). A clear downward trend was observed. A 4:1 MYR:Znmolar ratio suppressed occupation of site A almost completely. A secondbinding site was also affected by fatty acid binding (see D). (C)ITC curves for titrations of 500 μM MYR into 12.5 μM BSAor Zn1BSA. These titrations were carried out in H2O because of the insufficient solubility of MYR in Tris buffer. Thefits (Figure S9) correspond to a modelwith one set of binding sites to estimate the stoichiometry for thehighest-affinity sites. This equaled 5.0 ± 0.3, and the averagelog K was 6.3 ± 0.4 in the absence and 5.9 ±0.4 in the presence of Zn2+. More complex fits were possible,but the data were insufficient to justify them. (D) 111Cd NMR spectra of Cd2BSA recorded in the absence and presenceof 5 molar equiv of MYR. Peaks A and B were both suppressed by MYR.

Mentions: To address the suspected impact of chain length,we conducted furthercompetition experiments using the C14 fatty acid myristate (MYR).The binding of MYR to albumin (Figure S7) closely matches that of the physiologically most abundant palmitateand stearate in terms of binding sites12 but is slightly weaker.23 Titrationswith Zn2+ in the presence of increasing amounts of MYR(Figure 5A) revealed that the stoichiometry(Figure 5B) and/or affinity of Zn2+ decrease dramatically in the presence of >1 molar equiv of MYR.Conversely, MYR titrations of the 1:1 Zn:BSA complex showed that theenergetics but not the stoichiometry of the binding reaction are affectedby Zn2+, as indicated by a decrease in affinity and exothermicity(Figure 5C; ΔΔH = 1.1 kcal/mol, average for five Myr). These observations can berationalized by assuming that the binding of MYR requires the dissociationof Zn2+ from BSA; since the binding reaction is exothermic(ΔH = −4.7 kcal/mol), this dissociationmust be endothermic, although the difference in experimental conditionsprecludes direct quantitative comparisons.


A molecular mechanism for modulating plasma Zn speciation by fatty acids.

Lu J, Stewart AJ, Sleep D, Sadler PJ, Pinheiro TJ, Blindauer CA - J. Am. Chem. Soc. (2012)

Competitive binding ofmetals and MYR to BSA. (A) Effect of increasingamounts of MYR on the zinc-binding capacity of BSA. ITC curves fortitrations of 333 μM Zn2+ into 25 μM BSA inthe presence and absence of varying amounts (0–5 molar equiv)of MYR in 50 mM Tris/50 mM NaCl (pH 7.2). The fits (Figure S8) allowed estimates of the ratio of site A availability,as shown in (B). A clear downward trend was observed. A 4:1 MYR:Znmolar ratio suppressed occupation of site A almost completely. A secondbinding site was also affected by fatty acid binding (see D). (C)ITC curves for titrations of 500 μM MYR into 12.5 μM BSAor Zn1BSA. These titrations were carried out in H2O because of the insufficient solubility of MYR in Tris buffer. Thefits (Figure S9) correspond to a modelwith one set of binding sites to estimate the stoichiometry for thehighest-affinity sites. This equaled 5.0 ± 0.3, and the averagelog K was 6.3 ± 0.4 in the absence and 5.9 ±0.4 in the presence of Zn2+. More complex fits were possible,but the data were insufficient to justify them. (D) 111Cd NMR spectra of Cd2BSA recorded in the absence and presenceof 5 molar equiv of MYR. Peaks A and B were both suppressed by MYR.
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fig5: Competitive binding ofmetals and MYR to BSA. (A) Effect of increasingamounts of MYR on the zinc-binding capacity of BSA. ITC curves fortitrations of 333 μM Zn2+ into 25 μM BSA inthe presence and absence of varying amounts (0–5 molar equiv)of MYR in 50 mM Tris/50 mM NaCl (pH 7.2). The fits (Figure S8) allowed estimates of the ratio of site A availability,as shown in (B). A clear downward trend was observed. A 4:1 MYR:Znmolar ratio suppressed occupation of site A almost completely. A secondbinding site was also affected by fatty acid binding (see D). (C)ITC curves for titrations of 500 μM MYR into 12.5 μM BSAor Zn1BSA. These titrations were carried out in H2O because of the insufficient solubility of MYR in Tris buffer. Thefits (Figure S9) correspond to a modelwith one set of binding sites to estimate the stoichiometry for thehighest-affinity sites. This equaled 5.0 ± 0.3, and the averagelog K was 6.3 ± 0.4 in the absence and 5.9 ±0.4 in the presence of Zn2+. More complex fits were possible,but the data were insufficient to justify them. (D) 111Cd NMR spectra of Cd2BSA recorded in the absence and presenceof 5 molar equiv of MYR. Peaks A and B were both suppressed by MYR.
Mentions: To address the suspected impact of chain length,we conducted furthercompetition experiments using the C14 fatty acid myristate (MYR).The binding of MYR to albumin (Figure S7) closely matches that of the physiologically most abundant palmitateand stearate in terms of binding sites12 but is slightly weaker.23 Titrationswith Zn2+ in the presence of increasing amounts of MYR(Figure 5A) revealed that the stoichiometry(Figure 5B) and/or affinity of Zn2+ decrease dramatically in the presence of >1 molar equiv of MYR.Conversely, MYR titrations of the 1:1 Zn:BSA complex showed that theenergetics but not the stoichiometry of the binding reaction are affectedby Zn2+, as indicated by a decrease in affinity and exothermicity(Figure 5C; ΔΔH = 1.1 kcal/mol, average for five Myr). These observations can berationalized by assuming that the binding of MYR requires the dissociationof Zn2+ from BSA; since the binding reaction is exothermic(ΔH = −4.7 kcal/mol), this dissociationmust be endothermic, although the difference in experimental conditionsprecludes direct quantitative comparisons.

Bottom Line: Albumin transports both fatty acids and zinc in plasma.The molecular mechanism for this effect is likely due to a large conformational change elicited by fatty acid binding to a high-affinity interdomain site that disrupts at least one Zn site.Albumin may be a molecular device to "translate" certain aspects of the organismal energy state into global zinc signals.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK.

Show MeSH
Related in: MedlinePlus