Anchored LH2 Complexes in 2D Polarization Imaging

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• 作者：Sumera Tubasum ; Shunsuke Sakai ; Takehisa Dewa ; Villy Sundstr枚m ; Ivan G. Scheblykin ; Mamoru Nango ; T玫nu Pullerits
• 刊名：Journal of Physical Chemistry B
• 出版年：2013
• 出版时间：September 26, 2013
• 年：2013
• 卷：117
• 期：38
• 页码：11391-11396
• 全文大小：286K
• 年卷期：v.117,no.38(September 26, 2013)
• ISSN：1520-5207

文摘

Protein is a soft material with inherently large structural disorder. Consequently, the bulk spectroscopies of photosynthetic pigment protein complexes provide averaged information where many details are lost. Here we report spectroscopy of single light-harvesting complexes where fluorescence excitation and detection polarizations are both independently rotated. Two samples of peripheral antenna (LH2) complexes from Rhodopseudomonas acidophila were studied. In one, the complexes were embedded in polyvinyl alcohol (PVA) film; in the other, they were anchored on the glass surface and covered by the PVA film. LH2 contains two rings of pigment molecules鈥擝800 and B850. The B800 excitation polarization properties of the two samples were found to be very similar, indicating that orientation statistics of LH2s are the same in these two very different preparations. At the same time, we found a significant difference in B850 emission polarization statistics. We conclude that the B850 band of the anchored sample is substantially more disordered. We argue that both B800 excitation and B850 emission polarization properties can be explained by the tilt of the anchored LH2s due to the spin-casting of the PVA film on top of the complexes and related shear forces. Due to the tilt, the orientation statistics of two samples become similar. Anchoring is expected to orient the LH2s so that B850 is closer to the substrate. Consequently, the tilt-related strain leads to larger deformation and disorder in B850 than in B800.