M. Henriksson et al., Unordered structure of proinsulin C-peptide in aqueous solution and in thepresence of lipid vesicles, CELL MOL L, 57(2), 2000, pp. 337-342
Proinsulin C-peptide ameliorates renal and autonomic nerve function and inc
reases skeletal muscle blood flow, oxygen uptake and glucose transport in p
atients with insulin-dependent diabetes mellitus. These effects have in par
t been ascribed to the stimulatory influence of C-peptide on Na+, K+-ATPase
and endothelial nitric oxide synthase. To evaluate the capacity of C-pepti
de to insert into lipid bilayers and form ion channels, C-peptide secondary
structure and membrane interactions were studied with circular dichroism s
pectroscopy and size exclusion chromatography. C-peptide is shown to Lack a
stable secondary structure, both when part of proinsulin and when free in
aqueous solution, although the N-terminal third of the peptide exhibits an
alpha-helical conformation in trifluoroethanol. Moreover, C-peptide remains
disordered in the aqueous solvent in the presence of lipid vesicles, regar
dless of vesicle composition. In conclusion, C-peptide is unlikely to elici
t physiological effects through stable conformation-dependent interactions
with lipid membranes.