NMR and alanine scan studies of glucose-dependent insulinotropic polypeptide in water.
Glucose-dependent insulinotropic polypeptide (GIP) is an incretin hormone that stimulates the secretion of insulin after ingestion of food. GIP also promotes the synthesis of fatty acids in adipose tissue. Therefore, it is not surprising that numerous literature reports have shown that GIP is linked to diabetes and obesity-related diseases. In this study, we present the solution structure of GIP in water determined by NMR spectroscopy. The calculated structure is characterized by the presence of an alpha-helical motif between residues Ser(11) and Gln(29). The helical conformation of GIP is further supported by CD spectroscopic studies. Six GIP-(1-42)Ala(1-7) analogues were synthesized by replacing individual N-terminal residues with alanine. Alanine scan studies of these N-terminal residues showed that the GIP-(1-42)Ala(6) was the only analogue to show insulin-secreting activity similar to that of the native GIP. However, when compared with glucose, its insulinotropic ability was reduced. For the first time, these NMR and modeling results contribute to the understanding of the structural requirements for the biological activity of GIP.
Alaña
Iñigo
I
University College Dublin (UCD) School of Biomolecular and Biomedical Science, Centre for Synthesis and Chemical Biology, UCD Conway Institute, University College Dublin, Belfield, Dublin 4, Ireland.
Parker
Jeremy C
JC
Gault
Victor A
VA
Flatt
Peter R
PR
O'Harte
Finbarr P M
FP
Malthouse
J Paul G
JP
Hewage
Chandralal M
CM
D000409:Alanine / Q000737:chemistry*; D000595:Amino Acid Sequence; D000818:Animals; D005749:Gastric Inhibitory Polypeptide / Q000378:metabolism / Q000502:physiology*; D005947:Glucose / Q000378:metabolism*; D005973:Glutamine / Q000737:chemistry; D007328:Insulin / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000378:metabolism / Q000502:physiology*; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D051381:Rats; D012694:Serine / Q000737:chemistry
D007328:Insulin; D010446:Peptide Fragments; C101760:gastric inhibitory polypeptide (1-42); D005973:Glutamine; D012694:Serine; D005749:Gastric Inhibitory Polypeptide; D005947:Glucose; D000409:Alanine