The complex of cytochrome f and plastocyanin from Nostoc sp. PCC 7119 is highly dynamic.
Bottom Line: The complex from Nostoc sp.Chemical-shift-perturbation analysis showed that the presence of spin labels on the surface of Cyt f does not significantly affect the binding of Pc.The paramagnetic relaxation enhancement results are not consistent with a single orientation of Pc, thus indicating that multiple orientations must occur and suggesting that an encounter state represents a large fraction of the complex.
Affiliation: Institute of Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands.Show MeSH
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Mentions: The aim of this study was to gather distance restraints from PREs to refine thepublished solution structure. The residues selected for mutation to cysteine andtagging with the spin label are located around binding site for Pc on Cytf in the solution structure model. The spin labels at thesepositions were thus expected to yield PRE of nuclei on different sides of Pc.For this purpose, a spin label(1-oxyl-2,2,5,5-tetramethyl-δ-3-pyrroline-3-methyl)methanethiosulfonate(MTSL) was attached to the three Cyt f mutants, and the taggedprotein was added to Pc at a Cyt f/Pc molar ratio of 0.3:1.Under these conditions, the fraction of bound Pc was 24 %. Large PREswere observed already at this ratio for numerous Pc amide groups for eachvariant of Cyt f-MTSL, as illustrated in Figure 3.
Affiliation: Institute of Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands.