Malde Alpeshkumar K, Srivastava Sudha S, Coutinho Evans C
Department of Pharmaceutical Chemistry, Bombay College of Pharmacy, Kalina, Santacruz (E), Mumbai 400 098, India.
J Pept Sci. 2007 May;13(5):287-300. doi: 10.1002/psc.839.
Gastric inhibitory polypeptide (GIP, or glucose-dependent insulinotropic polypeptide) is a 42-amino acid incretin hormone moderating glucose-induced insulin secretion. Antidiabetic therapy based on GIP holds great promise because of the fact that its insulinotropic action is highly dependent on the level of glucose, overcoming the sideeffects of hypoglycemia associated with the current therapy of Type 2 diabetes. The truncated peptide, GIP(1-30)NH2, has the same activity as the full length native peptide. We have studied the structure of GIP(1-30)NH2 and built a model of its G-protein coupled receptor (GPCR). The structure of GIP(1-30)NH2 in DMSO-d6 and H2O has been studied using 2D NMR (total correlation spectroscopy (TOCSY), nuclear overhauser effect spectroscopy (NOESY), double quantum filtered-COSY (DQF-COSY), 13C-heteronuclear single quantum correlation (HSQC) experiments, and its conformation built by MD simulations with the NMR data as constraints. The peptide in DMSO-d6 exhibits an alpha-helix between residues Ile12 and Lys30 with a discontinuity at residues Gln19 and Gln20. In H2O, the alpha-helix starts at Ile7, breaks off at Gln19, and then continues right through to Lys30. GIP(1-30)NH2 has all the structural features of peptides belonging to family B1 GPCRs, which are characterized by a coil at the N-terminal and a long C-terminal alpha-helix with or without a break. A model of the seven transmembrane (TM) helices of the GIP receptor (GIPR) has been built on the principles of comparative protein modeling, using the crystal structure of bovine rhodopsin as a template. The N-terminal domain of GIPR has been constructed from the NMR structure of the N-terminal of corticoptropin releasing factor receptor (CRFR), a family B1 GCPR. The intra and extra cellular loops and the C-terminal have been modeled from fragments retrieved from the PDB. On the basis of the experimental data available for some members of family B1 GPCRs, four pairs of constraints between GIP(1-30)NH2 and its receptor were used in the FTDOCK program, to build the complete model of the GIP(1-30)NH2:GIPR complex. The model can rationalize the various experimental observations including the potency of the truncated GIP peptide. This work is the first complete model at the atomic level of GIP(1-30)NH2 and of the complex with its GPCR.
胃抑制多肽（GIP，即葡萄糖依赖性促胰岛素多肽）是一种由42个氨基酸组成的肠促胰岛素激素，可调节葡萄糖诱导的胰岛素分泌。基于GIP的抗糖尿病疗法前景广阔，因为其促胰岛素作用高度依赖于葡萄糖水平，克服了与2型糖尿病当前疗法相关的低血糖副作用。截短肽GIP(1-30)NH2具有与全长天然肽相同的活性。我们研究了GIP(1-30)NH2的结构，并构建了其G蛋白偶联受体（GPCR）的模型。使用二维核磁共振（全相关谱（TOCSY）、核Overhauser效应谱（NOESY）、双量子滤波相关谱（DQF-COSY）、13C-异核单量子相关（HSQC）实验）研究了GIP(1-30)NH2在氘代二甲亚砜（DMSO-d6）和水中的结构，并以核磁共振数据为约束条件通过分子动力学模拟构建其构象。在DMSO-d6中的该肽在Ile12和Lys30残基之间呈现α-螺旋，在Gln19和Gln20残基处有间断。在水中，α-螺旋从Ile7开始，在Gln19处中断，然后一直延续到Lys30。GIP(1-30)NH2具有属于B1类GPCR肽的所有结构特征，其特征是N端有一个卷曲结构，C端有一个长的α-螺旋，可能有间断也可能没有。基于比较蛋白质建模原理，以牛视紫红质的晶体结构为模板，构建了GIP受体（GIPR）的七跨膜（TM）螺旋模型。GIPR的N端结构域由促肾上腺皮质激素释放因子受体（CRFR，一种B1类GCPR）N端的核磁共振结构构建。细胞内和细胞外环以及C端由从蛋白质数据银行（PDB）检索到的片段建模。根据可获得的一些B1类GPCR成员的实验数据，在FTDOCK程序中使用了GIP(1-30)NH2与其受体之间的四对约束条件，构建了GIP(1-30)NH2:GIPR复合物的完整模型。该模型可以解释各种实验观察结果，包括截短的GIP肽的效力。这项工作是GIP(1-30)NH2及其与GPCR复合物在原子水平上的第一个完整模型。
