Negating coordinative cysteine and methionine residues during metathesis of unprotected peptides.

Ru-Alkylidene catalysed olefin metathesis generates metabolically stable cystine bridge peptidomimetics with defined geometry. Deleterious coordinative bonding to the catalyst by sulfur-containing functionality found in cysteine and methionine residues can be negated by and reversible oxidation of thiol and thioether functionality, as disulfides and S-oxides respectively, to facilitate high yielding ring-closing and cross metathesis of bioorthogonally protected peptides.

Characterisation of Elevenin-Vc1 from the Venom of : A Structural Analogue of α-Conotoxins.

Elevenins are peptides found in a range of organisms, including arthropods, annelids, nematodes, and molluscs. They consist of 17 to 19 amino acid residues with a single conserved disulfide bond. The subject of this study, elevenin-Vc1, was first identified in the venom of the cone snail ( , , 11-18).

Minimizing Mitogenic Potency of Insulin Analogues Through Modification of a Disulfide Bond.

The mechanisms by which insulin activates the insulin receptor to promote metabolic processes and cellular growth are still not clear. Significant advances have been gained from recent structural studies in understanding how insulin binds to its receptor. However, the way in which specific interactions lead to either metabolic or mitogenic signalling remains unknown.

Alkyne-Bridged α-Conotoxin Vc1.1 Potently Reverses Mechanical Allodynia in Neuropathic Pain Models.

Several -derived venom peptides are promising lead compounds for the management of neuropathic pain, with α-conotoxins being of particular interest. Modification of the interlocked disulfide framework of α-conotoxin Vc1.1 has been achieved using on-resin alkyne metathesis.

α-Conotoxin Peptidomimetics: Probing the Minimal Binding Motif for Effective Analgesia.

Several analgesic α-conotoxins have been isolated from marine cone snails. Structural modification of native peptides has provided potent and selective analogues for two of its known biological targets-nicotinic acetylcholine and γ-aminobutyric acid (GABA) G protein-coupled (GABA) receptors. Both of these molecular targets are implicated in pain pathways.

Probing the correlation between insulin activity and structural stability through introduction of the rigid A6-A11 bond.

The development of fast-acting and highly stable insulin analogues is challenging. Insulin undergoes structural transitions essential for binding and activation of the insulin receptor (IR), but these conformational changes can also affect insulin stability. Previously, we substituted the insulin A6-A11 cystine with a rigid, non-reducible C=C linkage ("dicarba" linkage).

Insulin in motion: The A6-A11 disulfide bond allosterically modulates structural transitions required for insulin activity.

The structural transitions required for insulin to activate its receptor and initiate regulation of glucose homeostasis are only partly understood. Here, using ring-closing metathesis, we substitute the A6-A11 disulfide bond of insulin with a rigid, non-reducible dicarba linkage, yielding two distinct stereo-isomers (cis and trans). Remarkably, only the cis isomer displays full insulin potency, rapidly lowering blood glucose in mice (even under insulin-resistant conditions).

Structure and activity of contryphan-Vc2: Importance of the d-amino acid residue.

In natural proteins and peptides, amino acids exist almost invariably as l-isomers. There are, however, several examples of naturally-occurring peptides containing d-amino acids. In this study we investigated the role of a naturally-occurring d-amino acid in a small peptide identified in the transcriptome of a marine cone snail.

A Naturally Occurring Peptide with an Elementary Single Disulfide-Directed β-Hairpin Fold.

Certain peptide folds, owing to a combination of intrinsic stability and resilience to amino acid substitutions, are particularly effective for the display of diverse functional groups. Such "privileged scaffolds" are valuable as starting points for the engineering of new bioactive molecules. We have identified a precursor peptide expressed in the venom gland of the marine snail Conus victoriae, which appears to belong to a hitherto undescribed class of molluscan neuropeptides.

Dicarba analogues of α-conotoxin RgIA. Structure, stability, and activity at potential pain targets.

α-Conotoxin RgIA is both an antagonist of the α9α10 nicotinic acetylcholine receptor (nAChR) subtype and an inhibitor of high-voltage-activated N-type calcium channel currents. RgIA has therapeutic potential for the treatment of pain, but reduction of the disulfide bond framework under physiological conditions represents a potential liability for clinical applications. We synthesized four RgIA analogues that replaced native disulfide pairs with nonreducible dicarba bridges.

Minimum active structure of insulin-like peptide 5.

Insulin-like peptide 5 (INSL5) is a complex two-chain peptide hormone constrained by three disulfide bonds in a pattern identical to insulin. High expression of INSL5 in the colon suggests roles in activation of colon motility and appetite control. A more recent study indicates it may have significant roles in the regulation of insulin secretion and β-cell homeostasis.

Dicarba α-conotoxin Vc1.1 analogues with differential selectivity for nicotinic acetylcholine and GABAB receptors.

Conotoxins have emerged as useful leads for the development of novel therapeutic analgesics. These peptides, isolated from marine molluscs of the genus Conus, have evolved exquisite selectivity for receptors and ion channels of excitable tissue. One such peptide, α-conotoxin Vc1.

Site-specific conjugation of a lanthanide chelator and its effects on the chemical synthesis and receptor binding affinity of human relaxin-2 hormone.

Diethylenetriamine pentaacetic acid (DTPA) is a popular chelator agent for enabling the labeling of peptides for their use in structure-activity relationship study and biodistribution analysis. Solid phase peptide synthesis was employed to couple this commercially available chelator at the N-terminus of either the A-chain or B-chain of H2 relaxin. The coupling of the DTPA chelator at the N-terminus of the B-chain and subsequent loading of a lanthanide (europium) ion into the chelator led to a labeled peptide (Eu-DTPA-(B)-H2) in low yield and having very poor water solubility.

Minimization of human relaxin-3 leading to high-affinity analogues with increased selectivity for relaxin-family peptide 3 receptor (RXFP3) over RXFP1.

Relaxin-3 is a neuropeptide that is implicated in the regulation of stress responses and memory. The elucidation of its precise physiological role(s) has, however, been hampered by cross-activation of the relaxin-2 receptor, RXFP1, in the brain. The current study undertook to develop analogues of human relaxin-3 (H3 relaxin) that can selectively bind and activate its receptor, RXFP3.

Structure and function relationship of murine insulin-like peptide 5 (INSL5): free C-terminus is essential for RXFP4 receptor binding and activation.

Insulin-like peptide 5 (INSL5) is a member of insulin/relaxin superfamily of peptides. It has recently been identified as the cognate ligand for the G-protein-coupled receptor, RXFP4. Although the complete physiological role of this naturally occurring peptide is still under investigation, there is evidence that it acts to both stimulate appetite and activate colon motility.

Use of a temporary "solubilizing" peptide tag for the Fmoc solid-phase synthesis of human insulin glargine via use of regioselective disulfide bond formation.

Solid-phase peptide synthesis has been refined to a stage where efficient preparation of long and complex peptides is now achievable. However, the postsynthesis handling of poorly soluble peptides often remains a significant hindrance to their purification and further use. Several synthetic schemes have been developed for the preparation of such peptides containing modifications to aid their solubility.