Structural Rearrangements in Chloroplast Thylakoid Membranes Revealed by Differential Scanning Calorimetry and Circular Dichroism Spectroscopy. Thermo-optic Effect
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- 作者：Anelia G. Dobrikova ; Zsuzsanna Vá ; rkonyi ; Sashka B. Krumova ; Lá ; szló ; Ková ; cs ; Georgi K. Kostov ; Svetla J. Todinova ; Mira C. Busheva ; Stefka G. Taneva ; and Gyozo Garab
- 刊名：Biochemistry
- 出版年：2003
- 出版时间：September 30, 2003
- 年：2003
- 卷：42
- 期：38
- 页码：11272 - 11280
- 全文大小：128K
- 年卷期：v.42,no.38(September 30, 2003)
- ISSN：1520-4995
文摘
The thermo-optic mechanism in thylakoid membranes was earlier identified by measuring thethermal and light stabilities of pigment arrays with different levels of structural complexity [Cseh, Z., etal. (2000) Biochemistry 39, 15250-15257]. (According to the thermo-optic mechanism, fast local thermaltransients, arising from the dissipation of excess, photosynthetically not used, excitation energy, induceelementary structural changes due to the "built-in" thermal instabilities of the given structural units.) Thesame mechanism was found to be responsible for the light-induced trimer-to-monomer transition in LHCII,the main chlorophyll a/b light-harvesting antenna of photosystem II (PSII) [Garab, G., et al. (2002)Biochemistry 41, 15121-15129]. In this paper, differential scanning calorimetry (DSC) and circulardichroism (CD) spectroscopy on thylakoid membranes of barley and pea are used to correlate the thermo-optically inducible structural changes with well-discernible calorimetric transitions. The thylakoidmembranes exhibited six major DSC bands, with maxima between about 43 and 87 
C. The heat sorptioncurves were analyzed both by mathematical deconvolution of the overall endotherm and by a successiveannealing procedure; these yielded similar thermodynamic parameters, transition temperature andcalorimetric enthalpy. A systematic comparison of the DSC and CD data on samples with different levelsof complexity revealed that the heat-induced disassembly of chirally organized macrodomains contributesprofoundly to the first endothermic event, a weak and broad DSC band between 43 and 48 C. Similarlyto the main macrodomain-associated CD signals, this low enthalpy band could be diminished by prolongedphotoinhibitory preillumination, the extent of which depended on the temperature of preillumination. Bymeans of nondenaturing, "green" gel electrophoresis and CD fingerprinting, it is shown that the secondmain endotherm, around 60 C, originates to a large extent from the monomerization of LHCII trimers.The main DSC band, around 70 C, which exhibits the highest enthalpy change, and another band around75-77 C relate to the dismantling of LHCII and other pigment-protein complexes, which underphysiologically relevant conditions cannot be induced by light. The currently available data suggest thefollowing sequence of events of thermo-optically inducible changes: (i) unstacking of membranes, followedby (ii) lateral disassembly of the chiral macrodomains and (iii) monomerization of LHCII trimers. Wepropose that thermo-optical structural reorganizations provide a structural flexibility, which is proportionalto the intensity of the excess excitation, while for their localized nature, the structural stability of thesystem can be retained.
C. The heat sorptioncurves were analyzed both by mathematical deconvolution of the overall endotherm and by a successiveannealing procedure; these yielded similar thermodynamic parameters, transition temperature andcalorimetric enthalpy. A systematic comparison of the DSC and CD data on samples with different levelsof complexity revealed that the heat-induced disassembly of chirally organized macrodomains contributesprofoundly to the first endothermic event, a weak and broad DSC band between 43 and 48 C. Similarlyto the main macrodomain-associated CD signals, this low enthalpy band could be diminished by prolongedphotoinhibitory preillumination, the extent of which depended on the temperature of preillumination. Bymeans of nondenaturing, "green" gel electrophoresis and CD fingerprinting, it is shown that the secondmain endotherm, around 60 C, originates to a large extent from the monomerization of LHCII trimers.The main DSC band, around 70 C, which exhibits the highest enthalpy change, and another band around75-77 C relate to the dismantling of LHCII and other pigment-protein complexes, which underphysiologically relevant conditions cannot be induced by light. The currently available data suggest thefollowing sequence of events of thermo-optically inducible changes: (i) unstacking of membranes, followedby (ii) lateral disassembly of the chiral macrodomains and (iii) monomerization of LHCII trimers. Wepropose that thermo-optical structural reorganizations provide a structural flexibility, which is proportionalto the intensity of the excess excitation, while for their localized nature, the structural stability of thesystem can be retained.