Purification and properties of cytochrome c-555 from phototrophic green sulfur bacteria

An isolated reaction center complex from the green sulfur bacterium Chlorobium vibrioforme can photoreduce ferredoxin at high rates

Chlorosome-depleted membranes and a reaction center complex with well-defined subunit composition were prepared from the green sulfur bacterium Chlorobium vibrioforme under anaerobic conditions. The reaction center complex contains a 15-kDa polypeptide with the N-terminal amino acid sequence MEPQLSRPETASNQVR/. This sequence is nearly identical to the N-terminus of the pscD gene product from Chlorobium limicola (Hager-Braun et al. (1995) Biochemistry 34: 9617-9624). In the presence of ferredoxin and ferredoxin:NADP(+) oxidoreductase, the membranes and the isolated reaction center complex photoreduced NADP(+) at rates of 333 and 110 μmol (mg bacteriochlorophyll a)(-1) h(-1), respectively. This shows that the isolated reaction center complex contains all the components essential for steady state electron transport. Midpoint potentials at pH 7.0 of 160 mV for cytochrome c 551 and of 245 mV for P840 were determined by redox titration. Antibodies against cytochrome c 551 inhibit NADP(+) reduction while antibodies against the bacteriochlorophyll a-binding Fenna-Matthews-Olson protein do not.

1H and 13C NMR assignment and secondary structure of Chlorobium limicola f. thiosulfatophilum ferrocytochrome c555

The 1H resonances of the ferrocytochrome c555 from the anaerobic green sulfur bacterium Chlorobium limicola f thio-sulfatophilum (strain Tassajara) have been assigned. Identification of spin systems and sequential assignment of 1H was accomplished by automated assignment computer programs followed by manual verification. In addition, 13C resonances have been extensively assigned by HSQC experiments at natural abundance. As determined by short-range NOE connectivities, 13C alpha chemical shifts, and HN exchange experiments, the secondary structure consists of 3 helices ranging from residues 3-13, 43-53 and 70-86. Interestingly, the second helix is significantly longer than observed by X-ray crystallography [1977, Proc. Natl. Acad. Sci. USA 74, 5244-5247]. A topological model of the cytochrome c555 is presented based on a small number of long-range NOE contacts. The helices are shown to pack onto the heme according to the pattern common to all class I cytochromes c.