Some characteristics of cytochrome f in the cyanobacterium Phormidium laminosum: its sequence and charge properties in the reaction with plastocyanin

Abstract

Part of the petCA operon was cloned and the sequence of the cytochrome f gene from the moderately thermophilic cyanobacterium Phormidium laminosum determined. A partial sequence of the petC gene encoding the Rieske iron-sulphur protein was also obtained. The cytochrome f gene encodes a mature protein of 385 residues and a leader sequence of 45 residues. The mature protein contains several acidic or neutral residues corresponding to basic residues in the turnip protein. Some of the latter are thought to be important for the interaction with plastocyanin via its "eastern' face. Many of the corresponding residues on the eastern face of P. laminosum plastocyanin are either basic or neutral instead of acidic. These comparisons suggested that the local charges on P. laminosum cytochrome f that are important for its interaction with the homologous plastocyanin may be negative rather than positive. The importance of acidic groups was confirmed by measuring the rates of reduction of horse heart cytochrome c and P. laminosum and spinach plastocyanins by the cytochrome bf complex isolated from P. laminosum. P. laminosum plastocyanin gave the highest rates, which decreased at high ionic strength, confirming the importance of positive local charges on this protein. When extrapolated to infinite ionic strength the rates observed with the two kinds of plastocyanin were similar, but cytochrome c became unreactive. An optimum was observed in the ionic strength response with P. laminosum plastocyanin.

The Ternary Complex of Cytochrome f and Cytochrome c: Identification of a Second Binding Site and Competition for Plastocyanin Binding

“…These results are in agreement with the work of Wagner et al, who have shown that the rate of reduction of horse cytc by intact cytochrome bf molecules from P. laminosum decreased sharply above an ionic strength of 70 mM. [28] Pc has a net charge of À 3 and does not form a complex with yeast cytc. In a previous 1 H NMR spectroscopy study, small chemical shift changes (< 0.05 ppm) were observed for horse cytc in the presence of pea plastocyanin.…”

The structure of plastocyanin from the cyanobacterium Phormidium laminosum

“…6). While the role of the invariant Tyr in physiological electron transfer is still uncertain, the presence of a basic region on the PlPc molecule is consistent with the observation that PlPc, when it reacts with the cytochrome b 6 f complex, behaves as though it has a small net positive local charge (Wagner et al, 1996).…”

“…PCC6803 occurs via a collisional mechanism has been attributed to the absence of an acidic patch (Romero et al, 1998). In the case of the weakly acidic (pI 5.2) plastocyanin from the cyanobacterium Phormidium laminosum, the effects of ionic strength on the reaction with the cytochrome b 6 f complex suggest that the electrostatic interactions found in plants are reversed, and that local positive charges on plastocyanin attract local negative charges on cytochrome f (Wagner et al, 1996). The need to explain this interaction in molecular terms led to an interest in the molecular structure and thus provided the motivation for the present work.…”

Computational approaches to structural and functional analysis of plastocyanin and other blue copper proteins

“…6), at least for the proteins in vitro [1, 3, 44 -45]. The more recent structure of bacterial Cyt f [35,46], on the contrary, does not show any basic ridges in the heme region and, as a whole, is far more negative than the eukaryotic species (net charge of cyanobacterial Cyt f: -12e vs. eukaryotic Cyt f: -1e), complementarily to its redox partner ( fig. 6).…”