Unordered structure of proinsulin C-peptide in aqueous solution and in the presence of lipid vesicles

Abstract

Proinsulin C-peptide ameliorates renal and autonomic nerve function and increases skeletal muscle blood flow, oxygen uptake and glucose transport in patients with insulin-dependent diabetes mellitus. These effects have in part been ascribed to the stimulatory influence of C-peptide on Na+,K+-ATPase and endothelial nitric oxide synthase. To evaluate the capacity of C-peptide to insert into lipid bilayers and form ion channels, C-peptide secondary structure and membrane interactions were studied with circular dichroism spectroscopy 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, regardless of vesicle composition. In conclusion, C-peptide is unlikely to elicit physiological effects through stable conformation-dependent interactions with lipid membranes.

C-Peptide Binding to Human Cell Membranes: Importance of Glu27

“…2). Moreover, the C-terminal tetrapeptide of rat C-peptide, VARQ, stimulates Na ϩ ,K ϩ -ATPase activity in rat renal tubular segments almost to the same extent as the full-length peptide or the C-terminal pentapeptide does (21), also suggesting that not only Glu dictates C-peptide action.…”

“…We could previously demonstrate stereospecific binding of C-peptide to intact human cells (19) and to solubilized cell membranes (20), using fluorescence correlation spectroscopy (FCS), while no C-peptide/lipid interactions could be observed by circular dichroism spectroscopy and size-exclusion chromatography (21). The binding of C-peptide to intact cells is displaceable both by full-length C-peptide and by a pentapeptide consisting of the five C-terminal amino acid residues of C-peptide (19).…”

Physiological effects and therapeutic potential of proinsulin C-peptide

“…It is negatively charged and not reported to show an ordered tertiary structure under physiological conditions (37). The amino acid sequence of C-peptide shows considerable variability between species, in contrast to the well-preserved molecular structure of insulin.…”

“…The amino acid sequence of C-peptide shows considerable variability between species, in contrast to the well-preserved molecular structure of insulin. However, in mammals the eight residues at positions 1, 3,6,11,12,21,27, and 31 of C-peptide are conserved or vary in only one species (37). Of these, Glu27 and Gln31 have been ascribed special importance for interaction between C-peptide and cell membranes (80).…”

Impact of Temperature Dependent Sampling Procedures in Proteomics and Peptidomics – A Characterization of the Liver and Pancreas Post Mortem Degradome

“…does not seem to posses any secondary structure in aqueous solutions (33), possibly making it more accessible to degradation and explaining the large number of C-peptide derivates detected whereas no other insulin peptides were detected. In rat, the mid-third region of the insulin-I C-peptide and the C-terminal penta-peptide (Fig.…”