Role of metal ions in the T- to R-allosteric transition in the insulin hexamer

Exploring the complex map of insulin polymorphism: a novel crystalline form in the presence ofm-cresol

In this study, the first crystal structure of a novel crystal form of human insulin bound tometa-cresol in an acidic environment is reported. The combination of single-crystal and powder X-ray diffraction crystallography led to the detection of a previously unknown monoclinic phase (P21). The structure was identified from the powder patterns and was solved using single-crystal diffraction data at 2.2 Å resolution. The unit-cell parameters at pH 6.1 area= 47.66,b = 70.36,c = 84.75 Å, β = 105.21°. The structure consists of two insulin hexamers per asymmetric unit. The potential use of this insulin form in microcrystalline drugs is discussed.

Functionality of an absolutely conserved glycine residue in the chimeric relaxin family peptide R3/I5

The insulin superfamily is a group of homologous proteins that are further divided into the insulin family and relaxin family according to their distinct receptors. All insulin superfamily members contain three absolutely conserved disulfide linkages and a nonchiral Gly residue immediately following the first B-chain cysteine. The functionality of this conserved Gly residue in the insulin family has been studied by replacing it with natural L-amino acids or the corresponding unnatural D-amino acids. However, such analysis has not been conducted on relaxin family members. In the present study, we conducted chiral mutagenesis on the conserved B11Gly of the chimeric relaxin family peptide R3/I5, which is an efficient agonist for receptor RXFP3 and RXFP4. Similar to the effects on insulin family foldability, L-Ala or L-Ser substitution completely abolished the in vitro refolding of a recombinant R3/I5 precursor; whereas, D-Ala or D-Ser substitution had no detrimental effect on refolding of a semi-synthetic R3/I5 precursor, suggesting that the conserved Gly residue controls the foldability of relaxin family members. In contrast to the effect on insulin family activity, D-Ala or D-Ser replacement had no detrimental effect on the binding and activation potencies of the mature R3/I5 towards both RXFP3 and RXFP4, suggesting that the conserved Gly residue is irrelevant to the relaxin family's activity. The present study revealed functionality of the conserved B-chain Gly residue for a relaxin family peptide for the first time, providing an overview of its contribution to foldability and activity of the insulin superfamily.

Evidence of oligomerization of bovine insulin in solution given by NMR

The protein hormone insulin exists in several forms in nature, and a large number of modified sequences are used in pharmacy. They differ by physicochemical properties and efficiency of biological action. Pancreatic bovine insulin was studied in an acidic solution by nuclear magnetic resonance spectroscopy. [Formula: see text]H and [Formula: see text]C NMR signal assignment of backbone and side chains was made by analysis of a set of 2D spectra obtained on a sample with natural isotope abundance. The presence of certain secondary structure elements was revealed on a qualitative level based on nuclear Overhauser effect spectroscopy, which are similar to those observed in the crystal structure. The C-terminus of the B-chain possessed a remarkable flexibility. The molecule was shown to exist in exchange with oligomers based on its self-diffusion coefficient and correlation time measurements performed at different concentrations. Certain signals in the NOESY and HSQC spectra are consistent with the presence of minor conformers; this is an obstacle in simulating the molecular structure under the conditions used in the experiment.

Selective oxidation of Zn2+—insulin catalyzed by Cu2+

The purpose of this study is to quantitate the sensitivity of Zn2+ -insulin to oxidation catalyzed by various redox active transition metals, Cu2+, Fe2+, Mn2+, Ni2+, Co2+, Cr3+. Human recombinant insulin (INS) was subjected to oxidation under various conditions in the presence and absence of Zn2+ and ascorbate. The extent of oxidation was monitored by RP-HPLC. Only Cu2+, but none of the other metals or combination thereof, for example, Ni2+/Co2+, Co2+/Cr3+, and Ni2+/Cr3+, catalyzed INS oxidation, for example, to an extent of 45% when 20 microM INS/8.8 microM Zn2+ were exposed to 8 microM Cu2+ and 50 microM ascorbate for 90 min. The Cu2+ -catalyzed oxidation mainly targeted the B chain of INS, where the two histidine residues are located.

Zinc induces dimerization of the class II major histocompatibility complex molecule that leads to cooperative binding to a superantigen

Dimerization of class II major histocompatibility complex (MHC) plays an important role in the MHC biological function. Mycoplasma arthritidis-derived mitogen (MAM) is a superantigen that can activate large fractions of T cells bearing specific T cell receptor Vbeta elements. Here we have used structural, sedimentation, and surface plasmon resonance detection approaches to investigate the molecular interactions between MAM and the class II MHC molecule HLA-DR1 in the context of a hemagglutinin peptide-(306-318) (HA). Our results revealed that zinc ion can efficiently induce the dimerization of the HLA-DR1/HA complex. Because the crystal structure of the MAM/HLA-DR1/hemagglutinin complex in the presence of EDTA is nearly identical to the structure of the complex crystallized in the presence of zinc ion, Zn(2+) is evidently not directly involved in the binding between MAM and HLA-DR1. Sedimentation and surface plasmon resonance studies further revealed that MAM binds the HLA-DR1/HA complex with high affinity in a 1:1 stoichiometry, in the absence of Zn(2+). However, in the presence of Zn(2+), a dimerized MAM/HLA-DR1/HA complex can arise through the Zn(2+)-induced DR1 dimer. In the presence of Zn(2+), cooperative binding of MAM to the DR1 dimer was also observed.

Ferric ions are essential for the biological activity of the hormone glycine-extended gastrin

Amidated and nonamidated gastrins elicit different biological effects via distinct receptors in different tissues. Amidated gastrin 17 stimulates gastric acid secretion and the development of gastric carcinoids, whereas glycine-extended gastrin 17 stimulates proliferation of the colonic mucosa and the development of colorectal cancers. Because glycine-extended gastrin 17 binds two ferric ions with high affinity (Baldwin, G. S., Curtain, C. C., and Sawyer, W. H. (2001) Biochemistry 40, 10741-10746), we have investigated the identity of the iron ligands and the role of ferric ions in biological activity. Here we report the solution structure of glycine-extended gastrin 17, determined by NMR spectroscopy. The spectral changes observed upon the addition of ferric ions revealed that Glu(7) acted as a ligand at the first ferric binding site, and that Glu(8) and Glu(9) acted as ligands at the second ferric ion binding site. Fluorescence quenching experiments confirmed that a GglyE7A mutant bound only one ferric ion. The inability of this mutant to stimulate proliferation or migration in the IMGE-5 cell line and the observation that the iron chelator desferrioxamine selectively blocked the effects of glycine-extended gastrin 17 indicated that binding of a ferric ion to Glu(7) was essential for biological activity. This is the first report of an essential role for a metal ion in the action of a hormone.