Analysis of pH-Induced Structural Changes of the Isolated Extrinsic 33 Kilodalton Protein of Photosystem II
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- 作者：T. Shutova ; K.-D. Irrgang ; V. Shubin ; V. V. Klimov ; and G. Renger
- 刊名：Biochemistry
- 出版年：1997
- 出版时间：May 27, 1997
- 年：1997
- 卷：36
- 期：21
- 页码：6350 - 6358
- 全文大小：176K
- 年卷期：v.36,no.21(May 27, 1997)
- ISSN：1520-4995
文摘
Structural properties of the isolated extrinsic regulatory 33 kDaprotein of the water-oxidizingcomplex were analyzed at different pH values. It was found that(a) titrations of the buffer capacityreveal a characteristic hysteresis effect that is unique for the 33 kDasubunit and is not observed for theother extrinsic proteins, (b) changes of the emission from thefluorescence probe 1,8-ANS are indicativeof an increased accessibility of the hydrophobic core of the 33 kDaprotein to the dye at lower pH, (c) thenear-UV circular dichroism spectrum of the polypeptide is altered owingto a pH decrease from 6.8 to 3.8and becomes drastically changed at pH 2.8, and (d) the content ofsecondary structure elements remainsvirtually constant in the range 3.8 < pH < 6.8, with the followingvalues gathered from far-UV CDspectra: ~8% 
-helix, ~33% 
beta2.gif" BORDER=0 ALIGN="middle">-strand, ~15% turns, and~44% random coil. Further acidification downto pH 2.8 gives rise to a decreased -helix and increased beta2.gif" BORDER=0 ALIGN="middle">-strandand random coil content. A theoreticalmodel [Ptitsyn, O., & Finkelstein, A. (1983) Biopolymers 2,15-22] was used to predict the probabilityand location of secondary structure elements within the proteinsequence. On the basis of these calculations,an extended hydrophobic beta2.gif" BORDER=0 ALIGN="middle">-sheet domain could exist in the center ofthe protein and an -helix in theC-terminal region. From these data, the 33 kDa protein is inferredto change its tertiary structure in vitroupon acidification of the aqueous environment. Possibleimplications of these features are discussed.
-helix, ~33% beta2.gif" BORDER=0 ALIGN="middle">-strand, ~15% turns, and~44% random coil. Further acidification downto pH 2.8 gives rise to a decreased -helix and increased beta2.gif" BORDER=0 ALIGN="middle">-strandand random coil content. A theoreticalmodel [Ptitsyn, O., & Finkelstein, A. (1983) Biopolymers 2,15-22] was used to predict the probabilityand location of secondary structure elements within the proteinsequence. On the basis of these calculations,an extended hydrophobic beta2.gif" BORDER=0 ALIGN="middle">-sheet domain could exist in the center ofthe protein and an -helix in theC-terminal region. From these data, the 33 kDa protein is inferredto change its tertiary structure in vitroupon acidification of the aqueous environment. Possibleimplications of these features are discussed.