A Non-Perturbative Molecular Grafting Strategy for Stable and Potent Therapeutic Peptide Ligands

Total Chemical Synthesis of Glucagon Glycoforms Reveals the Remarkable Influence of Natural Glycosylation

Glycosylation plays a critical role in modulating protein and peptide properties, yet the impact of recently discovered natural mucin-type O-glycosylation on therapeutic peptides like glucagon remains underexplored due to challenges in obtaining homogeneous research samples. Here, we address this challenge by developing a streamlined multistep synthesis-one purification protocol, enabling the production of 21 glucagon glycoforms with systematically varied glycosylation patterns. Investigation of these glycoforms revealed a remarkable impact of natural glycosylation on two properties critical for glucagon: solubility increased by over 870-fold, and fibrillation was completely inhibited, even under stringent conditions, while biological activity in elevating blood glucose levels was preserved. Computational analyses indicated that sialylated glycans disrupt intermolecular associations in the solid state, enhancing solubility, and shift secondary structures from β-sheets to α-helices, mitigating fibrillation. These findings suggest that glycosylation may have evolved as a natural mechanism to optimize undesirable properties, offering valuable insights for the development of therapeutics based on glucagon and other proteins and peptides with similar challenges.

Potent and Protease Resistant Azapeptide Agonists of the GLP-1 and GIP Receptors

The gut-derived peptide hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) play important physiological roles including glucose homeostasis and appetite suppression. Stabilized agonists of the GLP-1 receptor (GLP-1R) and dual agonists of GLP-1R and GIP receptor (GIPR) for the management of type 2 diabetes and obesity have generated widespread enthusiasm and have become blockbuster drugs. These therapeutics are refractory to the action of dipeptidyl peptidase-4 (DPP4), that catalyzes rapid removal of the two N-terminal residues of the native peptides, in turn severely diminishing their activity profiles. Here we report that a single atom change from carbon to nitrogen in the backbone of the entire peptide makes them refractory to DPP4 action while still retaining full potency and efficacy at their respective receptors. This was accomplished by use of aza-amino acids, that are bioisosteric replacements for α-amino acids that perturb the structural backbone and local side chain conformations. Molecular dynamics simulations reveal that aza-amino acid can populate the same conformational space that GLP-1 adopts when bound to the GLP-1R. The insertion of an aza-amino acid at the second position from the N-terminus in semaglutide and in a dual agonist of GLP-1R and GIPR further demonstrates its capability as a viable alternative to current DPP4 resistance strategies while offering additional structural variation that may influence downstream signaling.

Therapeutic stapled peptides: Efficacy and molecular targets

Peptide stapling, by employing a stable, preformed alpha-helical conformation, results in the production of peptides with improved membrane permeability and enhanced proteolytic stability, compared to the original peptides, and provides an effective solution to accelerate the rapid development of peptide drugs. Various reviews present peptide stapling chemistries, anchoring residues and one- or two-component cyclization, however, therapeutic stapled peptides have not been systematically summarized, especially focusing on various disease-related targets. This review highlights the latest advances in therapeutic peptide drug development facilitated by the application of stapling technology, including different stapling techniques, synthetic accessibility, applicability to biological targets, potential for solving biological problems, as well as the current status of development. Stapled peptides as therapeutic drug candidates have been classified and analysed mainly by receptor- and ligand-based stapled peptide design against various diseases, including cancer, infectious diseases, inflammation, and diabetes. This review is expected to provide a comprehensive reference for the rational design of stapled peptides for different diseases and targets to facilitate the development of therapeutic peptides with enhanced pharmacokinetic and biological properties.

Molecular design of peptide therapeutics via N-terminal modification

Glucagon-like peptide-1, glucose-dependent insulinotropic polypeptide, and glucagon are three naturally occurring peptide hormones that mediate glucoregulation. Several agonists representing appropriately modified native ligands have been developed to maximize metabolic benefits with reduced side-effects and many have entered the clinic as type 2 diabetes and obesity therapeutics. In this work, we describe strategies for improving the stability of the peptide ligands by making them refractory to dipeptidyl peptidase-4 catalyzed hydrolysis and inactivation. We describe a series of alkylations with variations in size, shape, charge, polarity, and stereochemistry that are able to engender full activity at the receptor(s) while simultaneously resisting enzyme-mediated degradation. Utilizing this strategy, we offer a novel method of modulating receptor activity and fine-tuning pharmacology without a change in peptide sequence.

A Robust Platform for the Molecular Design of Potent, Protease-Stable, Long-Acting GIP Analogues

Glucose-dependent insulinotropic peptide (GIP) is a 42-amino acid peptide hormone that regulates postprandial glucose levels. GIP binds to its cognate receptor, GIPR, and mediates metabolic physiology by improved insulin sensitivity, β-cell proliferation, increased energy consumption, and stimulated glucagon secretion. Dipeptidyl peptidase-4 (DPP4) catalyzes the rapid inactivation of GIP within 6 min in vivo. Here, we report a molecular platform for the design of GIP analogues that are refractory to DPP4 action and exhibit differential activation of the receptor, thus offering potentially hundreds of GIP-based compounds to fine-tune pharmacology. The lead compound from our studies, which harbored a combination of N-terminal alkylation and side-chain lipidation, was equipotent and retained full efficacy at GIPR as the native peptide, while being completely refractory toward DPP4, and was resistant to trypsin. The GIP analogue identified from these studies was further evaluated in vivo and is one of the longest-acting GIPR agonists to date.

Two-Chamber Aminocarbonylation of Aryl Bromides and Triflates Using Amino Acids as Nucleophiles

A palladium(0)-catalyzed aminocarbonylation reaction employing molybdenum hexacarbonyl as a carbon monoxide precursor for the production of N-capped amino acids using aryl and heteroaryl bromides and triflates is reported. The carbon monoxide is formed ex situ through the use of a two-chamber system, where carbon monoxide generated in one chamber is free to diffuse over and be consumed in the other palladium-catalyzed reaction chamber. Using this method, two series of aryl bromides and aryl triflates were utilized to synthesize 21 N-capped amino acids in isolated yields between 40 and 91%.

Hepatic Glucose Metabolism Disorder Induced by Adipose Tissue-Derived miR-548ag via DPP4 Upregulation

The present study aimed to explore the molecular mechanism underlying the regulation of glucose metabolism by miR-548ag. For the first time, we found that miR-548ag expression was elevated in the abdominal adipose tissue and serum of subjects with obesity and type 2 diabetes mellitus (T2DM). The conditional knockout of adipose tissue Dicer notably reduced the expression and content of miR-548ag in mouse adipose tissue, serum, and liver tissue. The combined use of RNAseq, an miRNA target gene prediction software, and the dual luciferase reporter assay confirmed that miR-548ag exerts a targeted regulatory effect on DNMT3B and DPP4. miR-548ag and DPP4 expression was increased in the adipose tissue, serum, and liver tissue of diet-induced obese mice, while DNMT3B expression was decreased. It was subsequently confirmed both in vitro and in vivo that adipose tissue-derived miR-548ag impaired glucose tolerance and insulin sensitivity by inhibiting DNMT3B and upregulating DPP4. Moreover, miR-548ag inhibitors significantly improved the adverse metabolic phenotype in both obese mice and db/db mice. These results revealed that the expression of the adipose tissue-derived miR-548ag increased in obese subjects, and that this could upregulate the expression of DPP4 by targeting DNMT3B, ultimately leading to glucose metabolism disorder. Therefore, miR-548ag could be utilized as a potential target in the treatment of T2DM.

Fluorine-induced polarity increases inhibitory activity of BPTI towards chymotrypsin

Substituting the P1 position in bovine pancreatic trypsin inhibitor (BPTI) is known to heavily influence its inhibitory activity towards serine proteases. Side-chain fluorinated aliphatic amino acids have been shown to alter numerous properties of peptides and proteins and thus are of interest in the context of BPTI. In our study, we systematically investigated the site-specific incorporation of non-canonical amino acids into BPTI by microwave-assisted solid-phase peptide synthesis (SPPS). Inhibitor activity of the variants was tested towards the serine protease α-chymotrypsin. We observed enhanced inhibition of two fluorinated BPTIs compared to wild type and hydrocarbon variants. To further investigate the complexes, we performed X-ray structure analysis. Our findings underline the power fluorine offers as a tool in protein engineering to beneficially alter the effects on phenomena as protein-protein interactions.