H-1 AND C-13 NMR ASSIGNMENT AND SECONDARY STRUCTURE OF CHLOROBIUM-LIMICOLA F THIOSULFATOPHILUM FERROCYTOCHROME C(555)

The H-1 resonances of the ferrocytochrome c(555) from the anaerobic gr een sulfur bacterium Chlorobium limicola f thiosulfatophilum (strain T assajara) have been assigned, Identification of spin systems and seque ntial assignment of H-1 was accomplished by automated assignment compu ter programs followed by manual verification, In addition,C-13 resonan ces have been extensively assigned by HSQC experiments at natural abun dance, As determined by short-range NOE connectivities,C-13(alpha) che mical shifts, and H-N exchange experiments, the secondary structure co nsists of 3 helices ranging from residues 3-13, 43-53 and 70-86, Inter estingly, 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 s mall number of long-range NOE contacts. The helices are shown to pack onto the heme according to the pattern common to all class I cytochrom es c.