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Mechanism of interaction of Al3+ with the proteins composition of photosystem II.

Hasni I, Yaakoubi H, Hamdani S, Tajmir-Riahi HA, Carpentier R - PLoS ONE (2015)

Bottom Line: The latter result was revealed by the drop of chlorophyll fluorescence emission spectra at low temperature (77 K), increase of F0 and confirmed by the native green gel electrophoresis.This was reflected by a major reduction of α-helix with an increase of β-sheet and random coil structures in Al 3+-PSII complexes.These structural changes are closely related with the functional alteration of PSII activity revealed by the inhibition of the electron transport chain of PSII.

View Article: PubMed Central - PubMed

Affiliation: Research Group in Plant Biology, Department of Chemistry, Biochemistry and Physics, University of Quebec at Trois-Rivieres, Trois-Rivieres, Quebec, Canada.

ABSTRACT
The inhibitory effect of Al3+on photosystem II (PSII) electron transport was investigated using several biophysical and biochemical techniques such as oxygen evolution, chlorophyll fluorescence induction and emission, SDS-polyacrylamide and native green gel electrophoresis, and FTIR spectroscopy. In order to understand the mechanism of its inhibitory action, we have analyzed the interaction of this toxic cation with proteins subunits of PSII submembrane fractions isolated from spinach. Our results show that Al 3+, especially above 3 mM, strongly inhibits oxygen evolution and affects the advancement of the S states of the Mn4O5Ca cluster. This inhibition was due to the release of the extrinsic polypeptides and the disorganization of the Mn4O5Ca cluster associated with the oxygen evolving complex (OEC) of PSII. This fact was accompanied by a significant decline of maximum quantum yield of PSII (Fv/Fm) together with a strong damping of the chlorophyll a fluorescence induction. The energy transfer from light harvesting antenna to reaction centers of PSII was impaired following the alteration of the light harvesting complex of photosystem II (LHCII). The latter result was revealed by the drop of chlorophyll fluorescence emission spectra at low temperature (77 K), increase of F0 and confirmed by the native green gel electrophoresis. FTIR measurements indicated that the interaction of Al 3+ with the intrinsic and extrinsic polypeptides of PSII induces major alterations of the protein secondary structure leading to conformational changes. This was reflected by a major reduction of α-helix with an increase of β-sheet and random coil structures in Al 3+-PSII complexes. These structural changes are closely related with the functional alteration of PSII activity revealed by the inhibition of the electron transport chain of PSII.

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Effect of the addition of various Al3+ concentrations in PSII submembrane fractions on the Chl fluorescence parameters.(A) F0; (B) Fm; (C) Fv/F0 and (D) Fv/Fm. The data are the mean ± SD of nine independent measurements.
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pone.0120876.g004: Effect of the addition of various Al3+ concentrations in PSII submembrane fractions on the Chl fluorescence parameters.(A) F0; (B) Fm; (C) Fv/F0 and (D) Fv/Fm. The data are the mean ± SD of nine independent measurements.

Mentions: In order to evaluate the effects of Al3+ in the electron transport chain of PSII, chlorophyll fluorescence parameters of PSII submembrane fractions are measured. Fig. 4 shows the variation of F0, the initial Chl fluorescence obtained in dark adapted samples, Fm, the maximal Chl fluorescence measured under saturating red-light illumination, the Fv/F0 and Fv/Fm ratios. Result in Fig. 4A shows an increase in F0 with increasing Al3+ concentrations. This effect was mainly marked above 2 mM. Nevertheless, with the same range of Al3+ concentrations, Fm registered a decline and reaches a larger decrease at higher levels of concentrations (above 2 mM) (Fig. 4B). The decline in Fm and the increase of F0 coincided with a strong decrease in both Fv/F0, a parameter that accounts for the simultaneous variations in Fm and F0 in determinations of the maximum quantum yields of PSII [70], and the maximal quantum yield of PSII (Fv/Fm) (Figs. 4C, 4D). Addition of low concentrations of Al3+ (below 2 mM) to the submembrane fractions of PSII did not affect significantly the values of the maximal PSII photochemical quantum yield, Fv/Fm. However, at the same range of Al3+ concentrations, Fv/F0 showed a significant decrease. In addition, Fv/Fm and Fv/F0 had obvious decreases with increasing concentrations of Al3+ above 2 mM, which can respectively reach 35% and 74% of reduction at 5 mM Al3+ compared to the control. This drop in Fv/F0 and Fv/Fm ratios observed with Al3+ concentrations correlates with the inhibition of oxygen evolution and the removal of the three extrinsic polypeptides associated with the OEC illustrated in Figs. 1 and 3, respectively.


Mechanism of interaction of Al3+ with the proteins composition of photosystem II.

Hasni I, Yaakoubi H, Hamdani S, Tajmir-Riahi HA, Carpentier R - PLoS ONE (2015)

Effect of the addition of various Al3+ concentrations in PSII submembrane fractions on the Chl fluorescence parameters.(A) F0; (B) Fm; (C) Fv/F0 and (D) Fv/Fm. The data are the mean ± SD of nine independent measurements.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4373732&req=5

pone.0120876.g004: Effect of the addition of various Al3+ concentrations in PSII submembrane fractions on the Chl fluorescence parameters.(A) F0; (B) Fm; (C) Fv/F0 and (D) Fv/Fm. The data are the mean ± SD of nine independent measurements.
Mentions: In order to evaluate the effects of Al3+ in the electron transport chain of PSII, chlorophyll fluorescence parameters of PSII submembrane fractions are measured. Fig. 4 shows the variation of F0, the initial Chl fluorescence obtained in dark adapted samples, Fm, the maximal Chl fluorescence measured under saturating red-light illumination, the Fv/F0 and Fv/Fm ratios. Result in Fig. 4A shows an increase in F0 with increasing Al3+ concentrations. This effect was mainly marked above 2 mM. Nevertheless, with the same range of Al3+ concentrations, Fm registered a decline and reaches a larger decrease at higher levels of concentrations (above 2 mM) (Fig. 4B). The decline in Fm and the increase of F0 coincided with a strong decrease in both Fv/F0, a parameter that accounts for the simultaneous variations in Fm and F0 in determinations of the maximum quantum yields of PSII [70], and the maximal quantum yield of PSII (Fv/Fm) (Figs. 4C, 4D). Addition of low concentrations of Al3+ (below 2 mM) to the submembrane fractions of PSII did not affect significantly the values of the maximal PSII photochemical quantum yield, Fv/Fm. However, at the same range of Al3+ concentrations, Fv/F0 showed a significant decrease. In addition, Fv/Fm and Fv/F0 had obvious decreases with increasing concentrations of Al3+ above 2 mM, which can respectively reach 35% and 74% of reduction at 5 mM Al3+ compared to the control. This drop in Fv/F0 and Fv/Fm ratios observed with Al3+ concentrations correlates with the inhibition of oxygen evolution and the removal of the three extrinsic polypeptides associated with the OEC illustrated in Figs. 1 and 3, respectively.

Bottom Line: The latter result was revealed by the drop of chlorophyll fluorescence emission spectra at low temperature (77 K), increase of F0 and confirmed by the native green gel electrophoresis.This was reflected by a major reduction of α-helix with an increase of β-sheet and random coil structures in Al 3+-PSII complexes.These structural changes are closely related with the functional alteration of PSII activity revealed by the inhibition of the electron transport chain of PSII.

View Article: PubMed Central - PubMed

Affiliation: Research Group in Plant Biology, Department of Chemistry, Biochemistry and Physics, University of Quebec at Trois-Rivieres, Trois-Rivieres, Quebec, Canada.

ABSTRACT
The inhibitory effect of Al3+on photosystem II (PSII) electron transport was investigated using several biophysical and biochemical techniques such as oxygen evolution, chlorophyll fluorescence induction and emission, SDS-polyacrylamide and native green gel electrophoresis, and FTIR spectroscopy. In order to understand the mechanism of its inhibitory action, we have analyzed the interaction of this toxic cation with proteins subunits of PSII submembrane fractions isolated from spinach. Our results show that Al 3+, especially above 3 mM, strongly inhibits oxygen evolution and affects the advancement of the S states of the Mn4O5Ca cluster. This inhibition was due to the release of the extrinsic polypeptides and the disorganization of the Mn4O5Ca cluster associated with the oxygen evolving complex (OEC) of PSII. This fact was accompanied by a significant decline of maximum quantum yield of PSII (Fv/Fm) together with a strong damping of the chlorophyll a fluorescence induction. The energy transfer from light harvesting antenna to reaction centers of PSII was impaired following the alteration of the light harvesting complex of photosystem II (LHCII). The latter result was revealed by the drop of chlorophyll fluorescence emission spectra at low temperature (77 K), increase of F0 and confirmed by the native green gel electrophoresis. FTIR measurements indicated that the interaction of Al 3+ with the intrinsic and extrinsic polypeptides of PSII induces major alterations of the protein secondary structure leading to conformational changes. This was reflected by a major reduction of α-helix with an increase of β-sheet and random coil structures in Al 3+-PSII complexes. These structural changes are closely related with the functional alteration of PSII activity revealed by the inhibition of the electron transport chain of PSII.

No MeSH data available.


Related in: MedlinePlus