E. Bouchayer et al., NMR and CD conformational studies of the C-terminal 16-peptides of Pseudomonas aeruginosa c(551) and Hydrogenobacter thermophilus c(552) cytochromes, J PEPT RES, 57(1), 2001, pp. 39-47
The 16-amino acid sequences of the C-terminal helices of the homologous bac
terial cytochromes C-551 from Pseudomonas aeruginosa and C-552 from Hydroge
nobacter thermophilus were synthesized and their solution structure studied
. Circular dichroism and NMR experiments in aqueous solution have shown the
presence of alpha -helices and 3(10)-helices. The populations of helical s
tructures in phosphate buffer, pH 3.5, 293 K, were 21% for C-551 and 20% fo
r C-552, but increased to 56.7 and 48%, respectively, in 50% aqueous 2,2,2-
trifluoroethanol. An isodichroic point was observed at 203 nm in CD spectra
for the helix/coil transition in mixtures of water/2, 2,2-trifluoroethanol
. NMR spectra in phosphate buffer show the presence of both alpha- and 3(10
)-helical structures. In water/2,2,2-trifluoroethanol (50:50) alpha -helice
s are predominant. CD temperature-dependency studies indicate that both pep
tides exhibit the same cooperativity for the transition in waterl 2,2,2-tri
fluoroethanol (50:50). The experimental data show that the amino acid subst
itutions do not favor heat resistance of the secondary structure of the C-5
52 C-terminal helix at the local level. Instead, they optimize nonlocal con
tacts of the polypeptide chain, which stabilize the tertiary structure in t
he native protein.