title: DPP IV resistance and insulin releasing activity of a novel di-substituted analogue of glucose-dependent insulinotropic polypeptide, (Ser2-Asp13)GIP.
abstract: Structure-function studies suggest that preservation of the N-terminus and secondary structure of glucose-dependent insulinotropic polypeptide (GIP) is important for biological activity. Therefore, a novel di-substituted analogue of GIP, (Ser(2)-Asp(13))GIP, containing a negatively charged Asp residue in place of an Ala in position 13, was synthesised and evaluated for in vitro biological activity. Incubation with dipeptidyl peptidase IV (DPP IV) showed the half-lives of GIP and (Ser(2)-Asp(13))GIP to be 2.3 and >4h, respectively. Insulin releasing studies in clonal pancreatic BRIN-BD11 cells demonstrated that (Ser(2)-Asp(13))GIP (10(-12)to 10(-7)mol/l) was significantly less potent (60-90%; P<0.05 to P<0.001) than native GIP. The peptide failed to display antagonistic properties as it did not significantly alter insulin secretion when incubated in the presence of GIP (10(-7)mol/l). These results demonstrate that despite increased resistance to DPP IV, substituting Ala in position 13 with a negatively charged Asp, thus producing the di-substituted analogue (Ser(2)-Asp(13))GIP, significantly reduces biological activity, most likely due to modifications within the secondary structure.
authors.affiliation: School of Biomedical Sciences, University of Ulster, Coleraine BT52 1SA, Northern Ireland, UK. va.gault@ulster.ac.uk
authors.forename: V A
authors.initials: VA
authors.lastname: Gault
authors.forename: N
authors.initials: N
authors.lastname: Irwin
authors.forename: P
authors.initials: P
authors.lastname: Harriott
authors.forename: P R
authors.initials: PR
authors.lastname: Flatt
authors.forename: F P M
authors.initials: FP
authors.lastname: O'Harte
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases / Q000378:metabolism*; D005749:Gastric Inhibitory Polypeptide / Q000138:chemical synthesis / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007340:Insulinoma; D007515:Islets of Langerhans / Q000166:cytology / Q000201:enzymology* / Q000378:metabolism; D017433:Protein Structure, Secondary; D051381:Rats; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014407:Tumor Cells, Cultured
chemical_list: D007328:Insulin; D005749:Gastric Inhibitory Polypeptide; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; C100151:dipeptidyl peptidase II