1 H and 13 C NMR assignment and secondary structure of Chlorobium limicola f. thiosulfatophilum ferrocytochrome c 555

The 1 H resonances of the ferrocytochrome c 555 from the anaerobic green sulfur bacterium Chlorobium limicola f thiosulfatophilum (strain Tassajara) have been assigned. Identification of spin systems and sequential assignment of 1 H was accomplished by automated assignment computer programs followed by manual verification. In addition, 13 C resonances have been extensively assigned by HSQC experiments at natural abundance. As determined by short‐range NOE connectivities, 13 C α chemical shifts, and H N 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 c 555 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 .