PDBsum entry 2axt

Electron transport

PDB id: 2axt

Contents

Protein chains

335 a.a.

488 a.a.

447 a.a.

340 a.a.

82 a.a.

35 a.a.

64 a.a.

35 a.a.

34 a.a.

37 a.a.

37 a.a.

36 a.a.

242 a.a.

30 a.a.

98 a.a.

137 a.a.

104 a.a.

62 a.a.

Ligands

CLA ×70

PHO ×4

PQ9 ×4

OEC ×2

BCR ×22

LHG ×2

SQD ×6

LMT ×6

MGE ×12

UNL ×34

DGD

BCT

HEM ×4

Metals

_CA

FE2

References listed in PDB file

Key reference

Title

Towards complete cofactor arrangement in the 3.0 a resolution structure of photosystem ii.

Authors

B.Loll, J.Kern, W.Saenger, A.Zouni, J.Biesiadka.

Ref.

Nature, 2005, 438, 1040-1044. [DOI no: 10.1038/nature04224]

PubMed id

16355230

Abstract

Oxygenic photosynthesis in plants, algae and cyanobacteria is initiated at photosystem II, a homodimeric multisubunit protein-cofactor complex embedded in the thylakoid membrane. Photosystem II captures sunlight and powers the unique photo-induced oxidation of water to atmospheric oxygen. Crystallographic investigations of cyanobacterial photosystem II have provided several medium-resolution structures (3.8 to 3.2 A) that explain the general arrangement of the protein matrix and cofactors, but do not give a full picture of the complex. Here we describe the most complete cyanobacterial photosystem II structure obtained so far, showing locations of and interactions between 20 protein subunits and 77 cofactors per monomer. Assignment of 11 beta-carotenes yields insights into electron and energy transfer and photo-protection mechanisms in the reaction centre and antenna subunits. The high number of 14 integrally bound lipids reflects the structural and functional importance of these molecules for flexibility within and assembly of photosystem II. A lipophilic pathway is proposed for the diffusion of secondary plastoquinone that transfers redox equivalents from photosystem II to the photosynthetic chain. The structure provides information about the Mn4Ca cluster, where oxidation of water takes place. Our study uncovers near-atomic details necessary to understand the processes that convert light to chemical energy.

Figure 3.
Figure 3: Redox-active cofactors and electron transfer chain. a, View along the membrane plane. The cofactors of the electron transfer chain (P[D1]/P[D2], Chl[D1]/Chl[D2], Pheo[D1]/Pheo[D2], Q[A]/Q[B]) are related by the pseudo-C2 axis (arrow). Fe^2+ (blue), Mn (red) and Ca^2+ (yellow) ions are shown as spheres. b, Schematic representation of the view in a. Selected distances (in angstroms) are drawn between cofactor centres (black lines) and edges of systems (red dotted lines).

Figure 4.
Figure 4: Oxygen-evolving centre. a, Electron density of the Mn[4]Ca cluster, viewed similarly to Fig. 3a. Surrounding amino acids of D1 (yellow) and CP43 (magenta) are indicated; Mn is red and Ca^2+ is orange. The 2F[o] - F[c] map is contoured at the 1.2 level. b, Schematic view of the Mn[4]Ca cluster. Distances between Mn (red) and Ca^2+ (orange) are indicated by the connecting lines (grey, 2.7 Å; blue, 3.3 Å, green, 3.4 Å). Amino acids of the first coordination sphere are black; those of the second sphere are grey; distances are given in angstroms. c, Superposition of the current Mn[4]Ca structure (coloured as in a) with that of ref. 5 (D1 in green, CP43 in orange, Mn in violet and Ca^2+ in yellow, respectively).

The above figures are reprinted by permission from Macmillan Publishers Ltd: Nature (2005, 438, 1040-1044) copyright 2005.