Research Article

Structure of a symmetric photosynthetic reaction center–photosystem

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Science  08 Sep 2017:
Vol. 357, Issue 6355, pp. 1021-1025
DOI: 10.1126/science.aan5611
  • Fig. 1 Overall structure of the HbRC.

    Structure as viewed from (A) the N-side or (B) within the membrane. The two PshA polypeptides are colored in red and pink. PshX subunits are colored in orange. Cofactor molecules are shown as stick models and colored teal (ET), blue (antenna), and lime (carotenoids). The [4Fe-4S] cluster is shown as red (Fe) and yellow (S) spheres. BChl and Chl tails have been truncated for clarity.

  • Fig. 2 Arrangement of the TMHs and pigments in the HbRC compared with PSI.

    (A) TMH arrangement of the HbRC and its superposition with the TMHs of PSI (N-side view). TMHs of the two PshA subunits are colored in red and pink and labeled 1 to 11, from N to C terminus. PshX helices are colored in orange and are labeled “X.” Transparent gray helices are from the heterodimeric core of PSI [Protein Data Bank (PDB) ID 1JB0]. (B) N-side view of the cofactor organization in the HbRC (colored) superimposed with the cofactors associated with the PsaA-PsaB heterodimeric core of PSI (transparent gray, PDB ID 1JB0). ET BChls and Chls are colored red, bulk antenna pigments are colored blue, and the three antenna BChl g that flank the ET chain are colored teal. BChl and Chl tails have been truncated for clarity.

  • Fig. 3 Cofactor arrangement of the ET chain.

    Coordinating residues belonging to one PshA of the homodimer are labeled and colored dark red, and those from the other PshA are colored pink. Cofactor carbons are colored differently to ease viewing: P800 (orange), Acc (green), and A0 (blue). The water molecule serving as an axial ligand to A0 is shown as a red ball, and the unidentified molecule of high electron density ligating Acc is shown as a purple ball. Center-to-center distances are labeled on the right side of the image. BChl and Chl tails have been truncated for clarity.

  • Fig. 4 Details of the ET cofactors and comparison with PSI.

    Magnified views of the interactions of PshA with the ET cofactors are shown in panels (A) P800 and Acc, (B) Acc and A0, and (C) A0 and FX. Center-to-center distances and ligands are labeled (see also table S2). Coordinating residues belonging to one PshA of the homodimer are labeled and colored dark red, and those from the other PshA are labeled and colored pink. Cofactor carbons are colored to facilitate viewing: P800 (orange), Acc (green), and A0 (blue). The axial ligands to A0 (water) and Acc (unknown) are shown as a red or purple ball, respectively. The center of the [4Fe-4S] cluster is represented by a black sphere. The corresponding cofactors of PSI are shown in transparent gray. BChl, Chl, and quinone tails have been truncated for clarity.

  • Fig. 5 Surface electrostatics models of the HbRC.

    Positive and negative charge are colored in blue and red, respectively (see scale at left). N-side (top) and P-side (bottom) surfaces of the HbRC are shown. The profile view (middle) reveals an asymmetric charge distribution creating an electrostatic field that would stabilize the charge-separated state (48); membrane boundaries are indicated by dashed lines. The PshB1 ferredoxin and cyt c553 structures shown to the right are multitemplate models based on sequence identity (see supplementary materials). Lys584 and Lys587 form a positively charged surface patch on each side of FX, whereas the side chains of Lys423 (marked) extend out from the HbRC further than any other residue.

Supplementary Materials

  • Structure of a symmetric photosynthetic reaction center–photosystem

    Christopher Gisriel, Iosifina Sarrou, Bryan Ferlez, John H. Golbeck, Kevin E. Redding, Raimund Fromme

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

    Download Supplement
    • Materials and Methods
    • Figs. S1 to S8
    • Tables S1 to S4
    • References

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