pH-dependent structural change of reduced spinach plastocyanin studied by perturbed angular correlation of gamma-rays and dynamic light scattering.
In this study the pH-dependent structural changes of reduced spinach plastocyanin were investigated using perturbed angular correlation (PAC) of gamma-rays and dynamic light scattering (DLS). PAC data of Ag-substituted plastocyanin indicated that the coordinating ligands are two histidine residues (His37, His87) and a cysteine residue (Cys84) in a planar configuration, whereas the methionine (Met92) found perpendicular to this plane is not a coordinating ligand at neutral pH. Two slightly different conformations with differences in the Cys-metal ion-His angles could be observed with PAC spectroscopy. At pH 5.3 a third coordination geometry appears which can be explained as the absence of the His87 residue and the coordination of Met92 as a ligand. With DLS the aggregation of reduced plastocyanin could be observed below pH 5.3, indicating that not only the metal binding site but also the aggregation properties of the protein change upon pH reduction. Both the structural changes at the metal binding site and the aggregation are shown to be reversible. These results support the hypothesis that the pH of the thylakoid lumen has to remain moderate during steady-state photosynthesis and indicate that low pH induced aggregation of plastocyanin might serve as a regulatory switch for photosynthesis.
Department of Natural Sciences, Royal Veterinary and Agricultural University, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark. kns@kvl.dk
Klára Nárcisz
KN
Sas
Anna
A
Haldrup
Lars
L
Hemmingsen
Eva
E
Danielsen
Lars Holm
LH
Øgendal
D001665:Binding Sites; D005720:Gamma Rays; D006863:Hydrogen-Ion Concentration; D008667:Metalloproteins / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism; D010970:Plastocyanin / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation / Q000528:radiation effects*; D012542:Scattering, Radiation; D018724:Spinacia oleracea / Q000737:chemistry
D008667:Metalloproteins; D045322:Photosynthetic Reaction Center Complex Proteins; D010940:Plant Proteins; D010970:Plastocyanin