Photosystem I at 4 Å resolution represents the first structural model of a joint photosynthetic reaction centre and core antenna system

Abstract

The 4 A X-ray structure model of trimeric photosystem I of the cyanobacterium Synechococcus elongatus reveals 31 transmembrane, nine surface and three stromal alpha-helices per monomer, assigned to the 11 protein subunits: PsaA and PsaB are related by a pseudo two-fold axis normal to the membrane plane, along which the electron transfer pigments are arranged. 65 antenna chlorophyll a (Chl a) molecules separated by < or = 16 A form an oval, clustered net continuous with the electron transfer chain through the second and third Chl a pairs of the electron transfer system. This suggests a dual role for these Chl a both in excitation energy and electron transfer. The architecture of the protein core indicates quinone and iron-sulphur type reaction centres to have a common ancestor.

Unaltered susceptibility to BSE in transgenic mice expressing human prion protein

“…The resulting map was restricted to a resolution of 8 Å by band-pass filtering of the Fourier transform. Figure 3d was prepared in the same way except that the starting point was a set of three-dimensional coordinates defining the ends of the ␣-helices identified in a 4-Å map derived from X-ray crystallography 8 . Polyalanine ␣-helices were constructed between the helix ends and the resulting PDB file was processed as for Fig.…”

Electrogenic reduction of the primary electron donor P700+ in photosystem I by redox dyes

“…The best resolution of the X-ray structural analysis of PSI crystals obtained at present (4 A) does not allow one to locate the primary electron donor P700 inside the protein complex unequivocally [3,5]. However, based on the c~-helical hydrophobic profile analysis [20], and on the studies of point mutations effects on the spectral and thermodynamic properties of P700 [21], the histidine residues were identified, which serve as additional ligands to Mg atoms in the primary donor P700 [22].…”

“…However, il is estimated that the overall process takes approximately 200 ns [4]. A recently published 4 A resolution X-ray structure of PS I complexes from the cyanobacterium 5),m'chococcus e/ongatus [5] suggests that an additional chlorophyll (z-monomer located near P700 at a distance comparable to that between centers of P700 dimer molecules ( 7.5 A) might take part in the electron transfer. The electron density map also shows two antenna chlorophylls, which are 13 and 15 /k distant from primary accepters A0 and A~.…”

Tansley Review No. 109.

“…PSI isolated from the cyanobacterium Synechococcus elongatus has been crystallized in Berlin by Witt and his collaborators (Witt et al, 1988 ;Krauss et al, 1996). These crystals have slowly been improved and now diffract X-rays to beyond 3 A / resolution (P. Fromme, pers.…”