title: The location of the mobile electron carrier ferredoxin in vascular plant photosystem I.
abstract: In this study, we present the location of the ferredoxin-binding site in photosystem I from spinach. Image analysis of negatively stained two-dimensional crystals indicates that the addition of ferredoxin and chemical cross-linkers do not significantly alter the unit cell parameters (for untreated photosystem I, a = 26.4 nm, b = 27.6 nm, and gamma = 90 degrees, space group p22(1)2(1) and for ferredoxin cross-linked photosystem I, a = 26.2 nm, b = 27.2 nm, and gamma = 90 degrees, space group p22(1)2(1)). Fourier difference analysis reveals that ferredoxin is bound on top of the stromal ridge principally interacting with the extrinsic subunits PsaC and PsaE. This location would be accessible to the stroma, thereby promoting efficient electron transfer away from photosystem I. This observation is significantly different from that of the ferredoxin binding site proposed for cyanobacteria. A model for the binding of ferredoxin in vascular plants is proposed and is discussed relative to observations in cyanobacteria.
authors.affiliation: Department of Biomolecular Sciences, University of Manchester Institute of Science and Technology (UMIST), Manchester, M60 1QD, UK.
authors.forename: S V
authors.initials: SV
authors.lastname: Ruffle
authors.forename: A O
authors.initials: AO
authors.lastname: Mustafa
authors.forename: A
authors.initials: A
authors.lastname: Kitmitto
authors.forename: A
authors.initials: A
authors.lastname: Holzenburg
authors.forename: R C
authors.initials: RC
authors.lastname: Ford
mesh_terms: D001665:Binding Sites; D003432:Cross-Linking Reagents; D003460:Crystallization; D000458:Cyanobacteria / Q000737:chemistry / Q000648:ultrastructure; D004579:Electron Transport; D005022:Ethyldimethylaminopropyl Carbodiimide / Q000031:analogs & derivatives / Q000378:metabolism; D005288:Ferredoxins / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure*; D005583:Fourier Analysis; D007091:Image Processing, Computer-Assisted; D008854:Microscopy, Electron; D008958:Models, Molecular; D009249:NADP / Q000378:metabolism; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure*; D045331:Photosystem I Protein Complex; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D011485:Protein Binding; D011487:Protein Conformation; D018724:Spinacia oleracea / Q000737:chemistry / Q000648:ultrastructure*
chemical_list: D003432:Cross-Linking Reagents; D005288:Ferredoxins; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D010940:Plant Proteins; D009249:NADP; C041829:1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide methiodide; D005022:Ethyldimethylaminopropyl Carbodiimide