Abstract:Spinach plastocyanin and turnip cytochrome f have been covalently linked by using a water-soluble carbodiimide to yield an adduct of the two proteins. The redox potential of cytochrome f in the adduct was shifted by -20 mV relative to that of free cytochrome f, while the redox potential of plastocyanin in the adduct was the same as that of free plastocyanin. Solvent perturbation studies showed the degree of heme exposure in the adduct to be less than in free cytochrome f, indicating that plastocyanin was linke… Show more
“…Also the reaction of plastocyanin with cytochrome c, acting as a non-physiological substitute for cytochromef, has been studied extensively. From this work it has emerged that PSI probably binds to both the northern and eastern sides of the molecule but reacts via the hydrophobic patch (Anderson et al, 1987;Takabe and Ishikawa, 1989;Nordling et al, 1991;Hervas et al, 1995), while cytochrome f and c bind and react via the acidic patch (Niwa et al, 1980;Augustin et al, 1983;Beoku-Betts et al, 1985;King et al, 1985;Anderson et al, 1987;Morand et al, 1989;Takabe and Ishikawa, 1989;Gross and Curtiss, 1991 ;He et al, 1991 ;Roberts et al, 1991 ;Christensen et al, 1992;Modi et al, 1992a,b;Meyer et al, 1993). The latter reaction complexes appear not to be static; KostiC and co-workers have tound evidence that a fast rearrangement of the partners within the cytochrome .…”
To compare cadmium-substituted plastocyanin with copper plastocyanin, the 'H-NMR spectra of CuI-, Curl-and Cd-plastocyanin from pea have been analyzed. Full assignments of the spectra of CuIand Cd-plastocyanin indicate chemical shift differences up to 1 ppm. The affected protons are located in the four loops that surround the Cu site. The largest differences were found for protons in the hydrogen bond network which stabilizes this part of the protein. This suggests that the chemical shift differences are caused by very small but extensive structural changes in the network upon replacement of CuI by Cd.For CuII-plastocyanin the resonances of 72% of the protons observed in the Cul form have been identified. Protons within =0.9 nm of the CuII were not observed due to fast paramagnetic relaxation. The protons between 0.9 -1.7 nm from the CuII showed chemical shift differences up to 0.4 ppm compared to both Cur-and Cd-plastocyanin. These differences can be predicted assuming that they represent pseudocontact shifts. When corrected for the pseudocontact shift contribution, the CuII-plastocyanin chemical shifts were nearly all identical within error to those of the Cd form, but not of the CuI-plastocyanin, indicating that the CuII-plastocyanin structure, in as far as it can be observed, resembles Cd-rather than CuI-plastocyanin. In a single stretch of residues (64-69) chemical shift differences remained between all three forms after correction.The fact that pseudocontact shifts were observed for protons which were not broadened may be attributable to the weaker distance dependence of the pseudocontact shift effect compared to paramagnetic relaxation. This results in two shells around the Cu atom, an inner paramagnetic shell (0-0.9 nm), in which protons are not observed due to broadening, and an outer paramagnetic shell (0.9-1.7 nm), in which protons can be observed and show pseudocontact shifts.Keywords: plastocyanin ; chemical shift; paramagnetic ; azurin ; cadmium.It is concluded that Cd-plastocyanin is a suitable redox-inactive substitute for Cu-plastocyanin.Plastocyanin is a small (10.4 kDa) type-I copper protein that functions as a soluble electron carrier in the lumen of thylakoid vesicles in chloroplasts. It shuttles electrons from the cytochrome lf complex to photosystem I (PSI), both of which are located in the thylakoid membrane. There is much interest in the question of how plastocyanin interacts with its redox partners. The protein has two obvious potential sites for electron transfer. First, the so-called hydrophobic patch at the top or north side of the protein in the conventional representation (Fig. 1) which provides the shortest route for the electron to reach the copper atom, via the ligand H87. Secondly, the acidic patch (at the east side) which requires a longer pathway for electron transfer (via ligand C84 and surface residue Y83) but contains two clusters of negative charges, which are potentially favourable for electrostatic interaction between plastocyanin and the redox partners.A variety of tec...
“…Also the reaction of plastocyanin with cytochrome c, acting as a non-physiological substitute for cytochromef, has been studied extensively. From this work it has emerged that PSI probably binds to both the northern and eastern sides of the molecule but reacts via the hydrophobic patch (Anderson et al, 1987;Takabe and Ishikawa, 1989;Nordling et al, 1991;Hervas et al, 1995), while cytochrome f and c bind and react via the acidic patch (Niwa et al, 1980;Augustin et al, 1983;Beoku-Betts et al, 1985;King et al, 1985;Anderson et al, 1987;Morand et al, 1989;Takabe and Ishikawa, 1989;Gross and Curtiss, 1991 ;He et al, 1991 ;Roberts et al, 1991 ;Christensen et al, 1992;Modi et al, 1992a,b;Meyer et al, 1993). The latter reaction complexes appear not to be static; KostiC and co-workers have tound evidence that a fast rearrangement of the partners within the cytochrome .…”
To compare cadmium-substituted plastocyanin with copper plastocyanin, the 'H-NMR spectra of CuI-, Curl-and Cd-plastocyanin from pea have been analyzed. Full assignments of the spectra of CuIand Cd-plastocyanin indicate chemical shift differences up to 1 ppm. The affected protons are located in the four loops that surround the Cu site. The largest differences were found for protons in the hydrogen bond network which stabilizes this part of the protein. This suggests that the chemical shift differences are caused by very small but extensive structural changes in the network upon replacement of CuI by Cd.For CuII-plastocyanin the resonances of 72% of the protons observed in the Cul form have been identified. Protons within =0.9 nm of the CuII were not observed due to fast paramagnetic relaxation. The protons between 0.9 -1.7 nm from the CuII showed chemical shift differences up to 0.4 ppm compared to both Cur-and Cd-plastocyanin. These differences can be predicted assuming that they represent pseudocontact shifts. When corrected for the pseudocontact shift contribution, the CuII-plastocyanin chemical shifts were nearly all identical within error to those of the Cd form, but not of the CuI-plastocyanin, indicating that the CuII-plastocyanin structure, in as far as it can be observed, resembles Cd-rather than CuI-plastocyanin. In a single stretch of residues (64-69) chemical shift differences remained between all three forms after correction.The fact that pseudocontact shifts were observed for protons which were not broadened may be attributable to the weaker distance dependence of the pseudocontact shift effect compared to paramagnetic relaxation. This results in two shells around the Cu atom, an inner paramagnetic shell (0-0.9 nm), in which protons are not observed due to broadening, and an outer paramagnetic shell (0.9-1.7 nm), in which protons can be observed and show pseudocontact shifts.Keywords: plastocyanin ; chemical shift; paramagnetic ; azurin ; cadmium.It is concluded that Cd-plastocyanin is a suitable redox-inactive substitute for Cu-plastocyanin.Plastocyanin is a small (10.4 kDa) type-I copper protein that functions as a soluble electron carrier in the lumen of thylakoid vesicles in chloroplasts. It shuttles electrons from the cytochrome lf complex to photosystem I (PSI), both of which are located in the thylakoid membrane. There is much interest in the question of how plastocyanin interacts with its redox partners. The protein has two obvious potential sites for electron transfer. First, the so-called hydrophobic patch at the top or north side of the protein in the conventional representation (Fig. 1) which provides the shortest route for the electron to reach the copper atom, via the ligand H87. Secondly, the acidic patch (at the east side) which requires a longer pathway for electron transfer (via ligand C84 and surface residue Y83) but contains two clusters of negative charges, which are potentially favourable for electrostatic interaction between plastocyanin and the redox partners.A variety of tec...
“…6, PC would bind through its acidic regions (residues 42-45 and 59-61 of spinach plastocyanin) on the side of the barrel to the basic region of cyt f around Lys-187, the copper would be at the bottom of the PC barrel in this binding geometry, and Tyr-83 would then be located closer to the heme than Asp-44. It should be noted that covalent cross-linking of the PC-cyt f pair renders it incompetent for intermolecular electron transfer (Qin and Kostic, 1993), and the PC inactive in the reduction of photosystem I (Morand et al, 1989).…”
mentioning
confidence: 99%
“…The smaller domain, consisting of residues 169-231, contains Lys-187, previously shown to cross-link to Asp-44 of plastocyanin (Morand et al, 1989;cf. Redinbo et al, this volume), that is solvent-exposed and 28 Å from the heme Fe (Fig.…”
The following findings concerning the structure of the cytochrome b 6 f complex and its component polypeptides, cyt b 6 , subunit IV and cytochrome f subunit are discussed:
1.Comparison of the amino acid sequences of 13 and 16 cytochrome b 6 and subunit IV polypeptides, respectively, led to (a) reconsideration of the helix lengths and probable interface regions, (b) identification of two likely surface-seeking helices in cyt b 6 and one in SU IV, and (c) documentation of a high degree of sequence invariance compared to the mitochondrial cytochrome. The extent of identity is particularly high (88% for conserved and pseudo-conserved residues) in the segments of cyt b 6 predicted to be extrinsic on the n-side of the membrane.
2.The intramembrane attractive forces between trans-membrane helices that normally stabilize the packing of integral membrane proteins are relatively weak.
3.The complex isolated in dimeric form has been visualized, along with isolated monomer, by electron microscopy. The isolated dimer is much more active than the monomer, is the major form of the complex isolated and purified from chloroplasts, and is inferred to be a functional form in the membrane.
4.The isolated cyt b 6 f complex contains one molecule of chlorophyll a.
5.The structure of the 252 residue lumen-side domain of cytochrome f isolated from turnip chloroplasts has been solved by X-ray diffraction analysis to a resolution of 2.3 Å.
“…Chemical cross-linking has implicated the interaction of a negatively charged region of spinach PC with both PS I and Cyt complexes. Specific cross-linking of spinach PC to lysine residues of turnip Cyt ƒ has been found (Morand et al, 1989), while the basic residues of a positively charged region within spinach PsaF have yet to be cataloged (Wynn et al, 1989;Hippler et al, 1989). From this initial analysis, electrostatic interaction between a negatively-charged domain of PC and a positively charged region on the membranebound redox partner has been proposed.…”
Section: Interaction Of Other Soluble Electron Donors With Photosymentioning
confidence: 95%
“…From this initial analysis, electrostatic interaction between a negatively-charged domain of PC and a positively charged region on the membranebound redox partner has been proposed. The contribution of this type of interaction is likely to be conserved because Euglena Cyt could also be covalently linked to turnip Cyt ƒ (Morand et al, 1989). However, a variety of cyanobacterial Cyt proteins and a cyanobacterial PC could not be crosslinked to turnip Cyt ƒ.…”
Section: Interaction Of Other Soluble Electron Donors With Photosymentioning
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.