SANS investigation of the photosynthetic machinery of Chloroflexus aurantiacus - PubMed (original) (raw)

SANS investigation of the photosynthetic machinery of Chloroflexus aurantiacus

Kuo-Hsiang Tang et al. Biophys J. 2010.

Abstract

Green photosynthetic bacteria harvest light and perform photosynthesis in low-light environments, and contain specialized antenna complexes to adapt to this condition. We performed small-angle neutron scattering (SANS) studies to obtain structural information about the photosynthetic apparatus, including the peripheral light-harvesting chlorosome complex, the integral membrane light-harvesting B808-866 complex, and the reaction center (RC) in the thermophilic green phototrophic bacterium Chloroflexus aurantiacus. Using contrast variation in SANS measurements, we found that the B808-866 complex is wrapped around the RC in Cfx. aurantiacus, and the overall size and conformation of the B808-866 complex of Cfx. aurantiacus is roughly comparable to the LH1 antenna complex of the purple bacteria. A similar size of the isolated B808-866 complex was suggested by dynamic light scattering measurements, and a smaller size of the RC of Cfx. aurantiacus compared to the RC of the purple bacteria was observed. Further, our SANS measurements indicate that the chlorosome is a lipid body with a rod-like shape, and that the self-assembly of bacteriochlorophylls, the major component of the chlorosome, is lipid-like. Finally, two populations of chlorosome particles are suggested in our SANS measurements.

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Figures

Figure 1

(A) The proposed photosystem. (B) Absorption spectra of the intact membrane, chlorosome, B808-866 complex, and RC of Cfx. aurantiacus.

Figure 2

SANS for the LH2 and RC of Rb. sphaeroides. (A) SANS data for LH2-LDAO mixtures in 0, 10, 20, 45, 80, and 100% D2O. (B) The Guinier fit for LH2-LDAO mixtures in different concentrations of D2O. Data are shifted along the y axis for comparison. (C) The normalized P(r) profile for LH2-LDAO mixtures in 45% (blue curve) and 10% D2O (red curve). (D) The SANS data for LH2-LDAO mixtures in 10% D2O (•) and the predicted SANS pattern (red line) calculated from the crystal structure for LH2 of Rps. acidophila. (E) The SANS data and Guinier fit (inset) for RC-LDAO mixtures in 100% D2O.

Figure 3

SANS for the B808-866 complex of Cfx. aurantiacus. (A) The SANS data for B808-866-_β_OG mixtures in 0, 17, 40, 80, and 100% D2O. (B) The SANS data and Guinier analysis (inset) for B808-866-_β_OG mixtures in 100% D2O. (C) The Guinier fit for B808-866-_β_OG mixtures in different concentrations of D2O. (D) The normalized P(r) profile for B808-866-_β_OG mixtures in 100% (black curve) and 17% D2O (red curve).

Figure 4

SANS for the chlorosome of Cfx. aurantiacus. (A) The SANS data for the chlorosome in 0, 25, 40, 60, 80, and 100% D2O at 20 mM Tris buffer at pH 8.0. (B) The total scattering intensity (I(0)) plot for the chlorosome in different concentrations of D2O. (C) The scattering data and Guinier analysis of the chlorosome in 100% D2O with two fits shown (inset). (D) The P(r) profile for the chlorosome in 100% D2O.

Figure 5

Comparisons of the SANS studies for B808-866 complex and RC of Cfx. aurantiacus and the crystal structure for LH1 and RC of Rps. palustris (PDB ID:

1PYH

). (A) The reconstructed model for the B808-866 complex and the crystal structure for the LH1 of Rps. palustris. (C) The reconstructed model for the RC of Cfx. aurantiacus and the crystal structure for the RC of Rps. palustris without the H-subunit. (B) The predicted SANS patterns calculated from the reconstructed model for the B808-866 complex and the crystal structure for the LH1 fit the data for B808-866-_β_OG mixtures in 17% D2O. (D) The predicted SANS patterns calculated from the reconstructed model for the RC of Cfx. aurantiacus and the crystal structure for the RC of Rps. palustris with or without the H-subunit fit the data for RC-LDAO mixtures in 5% D2O.

References

1. Blankenship R.E. Blackwell Science Ltd.; Oxford: 2002. Molecular Mechanisms of Photosynthesis.
1. Messinger J., Alia A., Govindjee Special educational issue on ‘Basics and application of biophysical techniques in photosynthesis and related processes’. Photosynth. Res. 2009;101:89–92. - PubMed
1. Thiyagarajan P., Tiede D.M. Detergent micelle structure and micelle-micelle interactions determined by small-angle neutron scattering under solution conditions used for membrane protein crystallization. J. Phys. Chem. 1994;98:10343–10351.
1. Owen T., Pynn R., Butler A. Metal-dependent self-assembly of a microbial surfactant. Langmuir. 2007;23:9393–9400. - PubMed
1. Mutch K.J., Duijneveldt J.S., Heenan R.K. Small-angle neutron scattering study of microemulsion-polymer mixtures in the protein limit. Langmuir. 2008;24:3053–3060. - PubMed

SANS investigation of the photosynthetic machinery of Chloroflexus aurantiacus - PubMed (original) (raw)