The role of the C-terminus of the insulin B-chain in modulating structural and functional properties of the hormone.
Within the scope of structure-function studies on the proteohormone insulin, the role of the C-terminal segment B26-B30 for self-association and receptor interaction was analyzed. Insulin derivatives with modifications in the region B26-B30 were synthesized by trypsin-catalyzed coupling reactions of des-(B23-B30)-insulin with synthetic peptides. The peptides were obtained by Fmoc solid-phase peptide synthesis. Insulins with multiple amino acid-->glycine substitutions were examined to distinguish between the influence of the side chains and the influence of the main chain in positions B27-B30 on the self-association of the hormone. The analogues [GlyB27,B28,B29,B30]insulin and [GlyB27,B28,B30]insulin exhibit relative receptor affinities of 80% and self-associate. The successive extension of [AlaB26]des-(B27-B30)-insulin-B26-amide (relative receptor binding 273%) with amino acids corresponding to the native sequence B27-B30 showed the influence of the length of the B-chain on receptor affinity: the extension by B27-threonine amide reduces receptor binding to 71%, all further prolongations have only small effects on the binding. The effect of the B28-side chain on main-chain conformation, self-association and receptor binding was examined with [XB28]des-(B29-B30)-insulin-B28-amides (X = Phe, Gly, D-Pro). While the glycine and D-proline analogues (relative binding 104 and 143%, respectively) retain the self-association properties typical of insulin, [PheB28]des-(B29-B30)-insulin-B28-amide (relative binding 50%) shows diminished self-association. The backbone-modified insulin derivative [SarB26]des-(B27-B30)-insulin-B26-amide (sarcosine = N-methylglycine) exhibits an unexpectedly high receptor affinity of 1100% which demonstrates that the B26-amide hydrogen of the native hormone is not important for receptor binding.
Leyer
S
S
German Wool Research Institute, Rheinisch-Westfälische Technische Hochschule Aachen, Germany.
Gattner
H G
HG
Leithäuser
M
M
Brandenburg
D
D
Wollmer
A
A
Höcker
H
H
D000595:Amino Acid Sequence; D002460:Cell Line; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D006801:Humans; D007328:Insulin / Q000737:chemistry* / Q000378:metabolism*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000737:chemistry*; D011487:Protein Conformation; D011972:Receptor, Insulin / Q000378:metabolism*; D013329:Structure-Activity Relationship; D014357:Trypsin / Q000378:metabolism
D007328:Insulin; D010446:Peptide Fragments; D011972:Receptor, Insulin; D014357:Trypsin