Specific Ca2+‐binding motif in the LH1 complex from photosynthetic bacterium Thermochromatium tepidum as revealed by optical spectroscopy and structural modeling

Department of Chemistry, Renmin University of China, Beijing, China.
FEBS Journal (Impact Factor: 3.99). 03/2009; 276(6):1739-49. DOI: 10.1111/j.1742-4658.2009.06905.x
Source: PubMed

ABSTRACT Native and Ca(2+)-depleted light-harvesting-reaction center core complexes (LH1-RC) from the photosynthetic bacterium Thermochromatium (Tch.) tepidum exhibit maximal LH1-Q(y) absorption at 915 and 889 nm, respectively. To understand the structural origins of the spectral variation, we performed spectroscopic and structure modeling investigations. For the 889 nm form of LH1-RC, bacteriochlorophyll a (BChl a) in the native form was found by means of near-infrared Fourier-transform Raman spectroscopy, a higher degree of macrocycle distortion and a stronger hydrogen bond with the beta-Trp(-8) residue. SWISS-MODEL structure modeling suggests the presence of a specific coordination motif of Ca(2+) at the C-terminus of the alpha-subunit of LH1, while MODELLER reveals the tilt of alpha- and beta-polypeptides with reference to the structural template, as well as a change in the concentric orientation of BChl a molecules, both of which may be connected to the long-wavelength LH1-Q(y) absorption of the 915 nm form. The carotenoid spirilloxanthin shows a twisted all-trans configuration in both forms of LH1 as evidenced by the resonance Raman spectroscopic results. With regard to the thermal stability, the 915 nm form was shown by the use of temperature-dependent fluorescence spectroscopy to be approximately 20 K more stable than the 889 nm form, which may be ascribed to the specific Ca(2+)-binding motif of LH1.

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    ABSTRACT: A three-dimensional all-atom structure of the LH1 light-harvesting complex of the photosynthetic center of the Thermochromatium tepidum bacteria was constructed with molecular modeling techniques.
    Moscow University Chemistry Bulletin 03/2013; 68(2). DOI:10.3103/S0027131413020077
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    Biochemistry 04/2011; 50(18):3638-48. DOI:10.1021/bi200278u · 3.01 Impact Factor
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    ABSTRACT: A three-dimensional model of subunit structure for the LH1 light-harvesting complex of the photosynthetic reaction center of Thermochromatium tepidum bacterium is constructed on the basis of the primary sequence of amino acid residues of the α-and β-polypeptide helixes; the specific binding site of the calcium ion is suggested. Keywordsphotosynthesis–light-harvesting complexes–three-dimensional polypeptide models–molecular mechanics
    Moscow University Chemistry Bulletin 04/2011; 66(2):80-82. DOI:10.3103/S0027131411020052
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