Zn2+-binding in the glutamate-rich region of the intrinsically disordered protein prothymosin-alpha

Recent Advances in Organic Small-Molecule Fluorescent Probes for the Detection of Zinc Ions (Zn2+)

Zinc(II) ions (Zn2g) play crucial roles in the growth, propagation, and metabolism of animals, plants, and humans. Abnormal concentrations of Zn2+ in the environment and living organisms pose potential risks to environmental protection and human health. Therefore, it is imperative to develop rapid, reliable and in-situ detection methods for Zn2+ in both environmental and biological contexts. Furthermore, effective analytical methods are required for diagnosing diseases and understanding physiological metabolic mechanisms associated with Zn2+ concentration levels. Organic small-molecule fluorescent probes offer advantages such as fast, reliable, convenient, non-destructive detection capabilities and have significant application potential in Zn2+ detection and bioimaging; thus garnering extensive attention. Over the past two years alone, various organic small-molecule probes for Zn2+ based on different detection mechanisms and fluorophores have been rapidly developed. However, these probes still exhibit several limitations that need further resolution. In light of this context, we provide a comprehensive summary of the detection mechanisms, performance characteristics, and application scope of Zn2+ fluorescence probes since year 2022 while highlighting their advantages. We also propose solutions to address existing issues with these probes and outline future directions for their advancement. This review aims to serve as a valuable reference source offering insights into the development of advanced organic small-molecule-based fluorescence probes specifically designed for detecting Zn2+.

Insight into Calcium-Binding Motifs of Intrinsically Disordered Proteins

Motifs within proteins help us categorize their functions. Intrinsically disordered proteins (IDPs) are rich in short linear motifs, conferring them many different roles. IDPs are also frequently highly charged and, therefore, likely to interact with ions. Canonical calcium-binding motifs, such as the EF-hand, often rely on the formation of stabilizing flanking helices, which are a key characteristic of folded proteins, but are absent in IDPs. In this study, we probe the existence of a calcium-binding motif relevant to IDPs. Upon screening several carefully selected IDPs using NMR spectroscopy supplemented with affinity quantification by colorimetric assays, we found calcium-binding motifs in IDPs which could be categorized into at least two groups-an Excalibur-like motif, sequentially similar to the EF-hand loop, and a condensed-charge motif carrying repetitive negative charges. The motifs show an affinity for calcium typically in the ~100 μM range relevant to regulatory functions and, while calcium binding to the condensed-charge motif had little effect on the overall compaction of the IDP chain, calcium binding to Excalibur-like motifs resulted in changes in compaction. Thus, calcium binding to IDPs may serve various structural and functional roles that have previously been underreported.

Structure of the Human ACP-ISD11 Heterodimer

In recent years, the mammalian mitochondrial protein complex for iron-sulfur cluster assembly has been the focus of important studies. This is partly because of its high degree of relevance in cell metabolism and because mutations of the involved proteins are the cause of several human diseases. Cysteine desulfurase NFS1 is the key enzyme of the complex. At present, it is well-known that the active form of NFS1 is stabilized by the small protein ISD11. In this work, the structure of the human mitochondrial ACP-ISD11 heterodimer was determined at 2.0 Å resolution. ACP-ISD11 forms a cooperative unit stabilized by several ionic interactions, hydrogen bonds, and apolar interactions. The 4'-phosphopantetheine-acyl chain, which is covalently bound to ACP, interacts with several residues of ISD11, modulating together with ACP the foldability of ISD11. Recombinant human ACP-ISD11 was able to interact with the NFS1 desulfurase, thus yielding an active enzyme, and the NFS1/ACP-ISD11 core complex was activated by frataxin and ISCU proteins. Internal motions of ACP-ISD11 were studied by molecular dynamics simulations, showing the persistence of the interactions between both protein chains. The conformation of the dimer is similar to that found in the context of the (NFS1/ACP-ISD11)₂ supercomplex core, which contains the Escherichia coli ACP instead of the human variant. This fact suggests a sequential mechanism for supercomplex consolidation, in which the ACP-ISD11 complex may fold independently and, after that, the NFS1 dimer would be stabilized.

Analysis of Metal Effects on C-Peptide Structure and Internalization

The connecting peptide (C-peptide) has received increased attention for its potential therapeutic effects in ameliorating illnesses such as kidney disease and diabetes. Although the mechanism of C-peptide signaling remains elusive, evidence supports its internalization and intracellular function. Emerging research is uncovering the diverse biological roles metals play in controlling and affecting the function of bioactive peptides. The work presented herein investigates interactions between C-peptide and first-row d-block transition metals, as well as their effects on C-peptide internalization into cells. Through spectroscopic techniques, it is demonstrated that Cr^III , Cu^II , and Zn^II bind to C-peptide with differing stoichiometries and biologically relevant affinities. In addition, metal binding elicits both subtle changes in secondary structure and inhibits adoption of an α-helical character in environments where the dielectric constants are reduced. This study shows how metal ions can modulate peptide hormone activity through subtle structural changes to disrupt cellular uptake.

Copper(II)-Binding Induces a Unique Polyproline Type II Helical Structure within the Ion-Binding Segment in the Intrinsically Disordered F-Domain of Ecdysteroid Receptor from Aedes aegypti

Reproduction of the dominant vector of Zika and dengue diseases, Aedes aegypti mosquito, is controlled by an active heterodimer complex composed of the 20-hydroxyecdysone receptor (EcR) and ultraspiracle protein. Although A. aegypti EcR shares the structural and functional organization with other nuclear receptors, its C-terminus has an additional long F domain (AaFEcR). Recently, we showed that the full length AaFEcR is intrinsically disordered with the ability to specifically bind divalent metal ions. Here, we describe the details of the exhaustive structural and thermodynamic properties of Zn²⁺- and Cu²⁺-complexes with the AaFEcR domain, based on peptide models of its two putative metal binding sites (Ac-HGPHPHPHG-NH₂ and Ac-QQLTPNQQQHQQQHSQLQQVHANGS-NH₂). Unexpectedly, only in the presence of increasing concentrations of Cu²⁺ ions, the Ac-HGPHPHPHG-NH₂ peptide gained a metal ion-induced poly-l-proline type II helical structure, which is unique for members of the family of nuclear receptors.