The conformation of eukaryotic cytochrome c around residues 39, 57, 59 and 74

Abstract

1H-n.m.r. studies of horse, tuna, Candida krusei and Saccharomyces cerevisiae cytochromes c showed that each of the proteins contains a similar cluster of residues at the bottom of the protein that assists in shielding the haem from the solvent. The relative positions of the residues forming these clusters vary continuously with temperature, and they change with the change in protein redox state. This conformational heterogeneity is discussed with reference to the conformational flexibility of cytochrome c around residues 57, 59 and 74. Spectroscopic measurements of pKa values for Lys-55 (horse and tuna cytochromes c) and His-33 and His-39 (C. krusei and S. cerevisiae cytochromes c) are in excellent agreement with expectations based on chemical-modification studies of horse cytochrome c. [Bosshard & Zürrer (1980) J. Biol. Chem. 255, 6694-6699] and on the X-ray-crystallographic structure of tuna cytochrome c [Takano & Dickerson (1981) J. Mol. Biol. 153, 79-94, 95-115].

Role of arginine-38 in regulation of the cytochrome c oxidation-reduction equilibrium

“…This similarity indicates that heme methyl-8, heme propionate-7, and Trp-59 have a similar spatial arrangement in all of the proteins. None of the heme resonances monitored were significantly shifted by varying pH* in a similar way to Cutler et al The pK values stated are accurate to h0.1 pK unit except for those of the Cys-102/Arg-38 protein which were previously reported to be accurate to f0.2 pK unit (Robinson et al, 1983). resonances of bacterial cytochromes whose heme propionate substituents titrated Leitch et al, 1984).…”

“…The His-39 pKa values are important because their redox state shift is a reflection of the oxidation state conformational change (Robinson et al, 1983). Thus, all the proteins undergo an oxidation state linked conformational change.…”

Modulation of the alkaline transition in cytochrome c and cytochrome c-T by full or specific partial acetimidylation

“…Wallace, 1984), that shows the alkaline-transition characteristics of acetimidyl-cytochrome c. N.m.r. observations of cytochrome c on varying the pH over the range of the alkaline transition show no evidence of major structural reorganization Robinson et al, 1983), so that the substitute lysine ligand must lie close to the haem group. The obvious candidates are Lys-79 or, at a slightly greater distance, Lys-72.…”

13C‐NMR studies of horse ferrocytochrome c

“…NMR spectra were obtained using a Bruker AM300 spectrometer operating at 300.13 MHz for protons and 75.47 MHz for carbon. Since the use of proton decoupling causes significant sample heating, the equilibrium temperature established in each experiment was measured by acquiring a proton spectrum within 5 s to determine the shift of the 6CH3 of Ile-57, which has a large and approximately linear temperature dependence in the range studied [14]. Proton decoupling by means of a train of 180" pulses [17] was used to minimise the heating effect for spectra obtained below 50°C.…”