Elucidation of a Copper Binding Site in Proinsulin C-peptide and Its Implications for Metal-Modulated Activity

Optimizing expression, purification, structural and functional assessments of a novel dimeric incretin (GLP-1cpGLP-1)

Glucagon-like peptide-1 (GLP-1) is an incretin hormone that reduces postprandial glycemic excursions by enhancing insulin secretion. In this study, a new dimeric GLP-1 analogue (GLP-1cpGLP-1) was designed by inserting human insulin C-peptide (CP) in the middle of a dimer of [Gly8] GLP-1 (7-36). Then, the dimeric incretin (GLP-1cpGLP-1) was ligated to human αB-crystallin (αB-Cry) to create a hybrid protein, abbreviated as αB-GLP-1cpGLP-1. The constructed gene was well expressed in the bacterial host system. After specific chemical release from the hybrid protein, the dimeric incretin was purified by size exclusion chromatography (SEC). Finally, the RP-HPLC analysis indicated a purity of >99 % for the dimeric incretin. The secondary structure assessments by various spectroscopic methods, and in silico analysis suggested that the dimeric incretin has α-helical rich structure. The dynamic light scattering (DLS) analysis indicates that our dimeric incretin forms large oligomeric structures. This incretin analogue significantly reduced blood glucose levels in both healthy and diabetic mice while effectively triggering insulin release. The size exclusion HPLC also indicates the interaction of the new incretin analogue with human serum albumin, the main carrier protein in the bloodstream. Consistent with the results obtained from the biological activity assessments, this significant interaction indicates its potential as a viable therapeutic agent with a long-lasting effect. The results of our research represent a significant breakthrough in the successful design of an active incretin dimer capable of effectively controlling blood sugar levels and inducing insulin secretion in the realm of diabetes treatment.

Copper(II) coordination to the intrinsically disordered region of SARS-CoV-2 Nsp1

The intrinsically disordered C-terminal peptide region of severe acute respiratory syndrome coronavirus 2 nonstructural protein-1 (Nsp1-CT) inhibits host protein synthesis by blocking messenger RNA (mRNA) access to the 40S ribosome entrance tunnel. Aqueous copper(II) ions bind to the disordered peptide with micromolar affinity, creating a possible strategy to restore protein synthesis during host infection. Electron paramagnetic resonance (EPR) and tryptophan fluorescence measurements on a 10-residue model of the disordered protein region (Nsp1-CT10), combined with advanced quantum mechanics calculations, suggest that the peptide binds to copper(II) as a multidentate ligand. Two optimized computational models of the copper(II)-peptide complexes were derived: One corresponding to pH 6.5 and the other describing the complex at pH 7.5 to 8.5. Simulated EPR spectra based on the calculated model structures are in good agreement with experimental spectra.

Peptide-based probe for colorimetric and fluorescent detection of Cu2+ and S2- in environmental and biological systems

Pollution caused by Copper and hydrogen sulfide pollution has severe adverse effects on the environment and organisms. Real-time, fast and accurate monitoring of Cu2+ and S2- faces serious challenges. In this study, we designed a novel biosensor and synthesized it by mimicking the structure of the main Cu(II)-binding site on bovine serum albumin. As a peptide-based sensor, FGGH (FITC-Gly-Gly-His-NH2) can perform the sequential detection of Cu2+ and S2- by fluorescence and colorimetry. The high water solubility and selectivity make it suitable for monitoring Cu2+ and S2- in environmental water samples with high sensitivity; its limit of detection (LOD) is as low as 1.42 nM for Cu2+ and 22.2 nM for S2-. The paper-based sensing platform of this probe was found to be a promising tool for the on-site visualization of real-time quantitative analysis of Cu2+ and S2- due to its rapid response and recyclable detection characteristics. Additionally, FGGH was successfully used to image Cu2+ and S2- in living cells and zebrafish models with adequate fluorescence stability and low cytotoxicity, providing the first visual evidence of the effect of the interactions between Cu2+ and S2- on the redox homeostasis of organisms.

A voltammetric peptide biosensor for Cu2+ metal ion quantification in coffee seeds

A prion-derived copper(II)-binding peptide was assembled onto a gold electrode for the building of a voltammetric biosensor for measuring the Cu2+ metal ion in biological samples. The chosen sequence was H-CVNITKQHTVTTTT-NH2, with an appended cysteine residue for binding to the gold surface as a self-assembled monolayer and a histidine residue as the anchorage point for copper(II) complexation. The biosensor showed a linear range of 10-7 to 10-6 M with an 8.0 × 10-8 M detection limit and a 1.0 × 10-7 M quantification limit, with good precision, trueness, and absence of matrix effect. The quantification of Cu2+ was performed in the presence of other transition metal ions, such as Zn2+, Cd2+, Fe2+, or Ni2+, which indicates the excellent selectivity of the biosensor. When the modified electrode was applied for measuring copper(II) in calcined coffee seeds, a difference in copper amount was observed between two Coffea arabica cultivars that were submitted to a treatment with a copper-based antifungal, showing the applicability of the biosensor in the agricultural field.

Characterizing metal-biomolecule interactions by mass spectrometry

Metal micronutrients are essential for life and exist in a delicate balance to maintain an organism's health. The labile nature of metal-biomolecule interactions clouds the understanding of metal binders and metal-mediated conformational changes that are influential to health and disease. Mass spectrometry (MS)-based methods and technologies have been developed to better understand metal micronutrient dynamics in the intra- and extracellular environment. In this review, we describe the challenges associated with studying labile metals in human biology and highlight MS-based methods for the discovery and study of metal-biomolecule interactions.

Copper(II) Affects the Biochemical Behavior of Proinsulin C-peptide by Forming Ternary Complexes with Serum Albumin

Peptide hormones are essential signaling molecules with therapeutic importance. Identifying regulatory factors that drive their activity gives important insight into their mode of action and clinical development. In this work, we demonstrate the combined impact of Cu(II) and the serum protein albumin on the activity of C-peptide, a 31-mer peptide derived from the same prohormone as insulin. C-peptide exhibits beneficial effects, particularly in diabetic patients, but its clinical use has been hampered by a lack of mechanistic understanding. We show that Cu(II) mediates the formation of ternary complexes between albumin and C-peptide and that the resulting species depend on the order of addition. These ternary complexes notably alter peptide activity, showing differences from the peptide or Cu(II)/peptide complexes alone in redox protection as well as in cellular internalization of the peptide. In standard clinical immunoassays for measuring C-peptide levels, the complexes inflate the quantitation of the peptide, suggesting that such adducts may affect biomarker quantitation. Altogether, our work points to the potential relevance of Cu(II)-linked C-peptide/albumin complexes in the peptide's mechanism of action and application as a biomarker.

Quantifying the Binding Interactions Between Cu(II) and Peptide Residues in the Presence and Absence of Chromophores

Copper(II) is an essential metal in biological systems, conferring unique chemical properties to the biomolecules with which it interacts. It has been reported to directly bind to a variety of peptides and play both necessary and pathological roles ranging from mediating structure to electron transfer properties to imparting catalytic function. Quantifying the binding affinity and thermodynamics of these Cu(II)-peptide complexes in vitro provides insight into the thermodynamic driving force of binding, potential competitions between different metal ions for the peptide or between different peptides for Cu(II), and the prevalence of the Cu(II)-peptide complex in vivo. However, quantifying the binding thermodynamics can be challenging due to a myriad of factors, including accounting for all competing equilibria within a titration experiment, especially in cases where there are a lack of discrete spectroscopic handles representing the peptide, the d-block metal ion, and their interactions. Here, a robust set of experiments is provided for the accurate quantification of Cu(II)-peptide thermodynamics. This article focuses on the use of electronic absorption spectroscopy in the presence and absence of chromophoric ligands to provide the needed spectroscopic handle on Cu(II) and the use of label-free isothermal titration calorimetry. In both experimental techniques, a process is described to account for all competing equilibria. While the focus of this article is on Cu(II), the described set of experiments can apply beyond Cu(II)-peptide interactions, and provide a framework for accurate quantification of other metal-peptide systems under physiologically relevant conditions.