Single-Molecule Force Spectroscopy Reveals the Dynamic HgS Coordination Site in the De Novo-Designed Metalloprotein α3DIV

Enzymatic Protein Immobilization for Nanobody Array

Antibody arrays play a pivotal role in the detection and quantification of biomolecules, with their effectiveness largely dependent on efficient protein immobilization. Traditional methods often use heterobifunctional cross-linking reagents for attaching functional residues in proteins to corresponding chemical groups on the substrate surface. However, this method does not control the antibody's anchoring point and orientation, potentially leading to reduced binding efficiency and overall performance. Another method using anti-antibodies as intermediate molecules to control the orientation can be used but it demonstrates lower efficiency. Here, we demonstrate a site-specific protein immobilization strategy utilizing OaAEP1 (asparaginyl endopeptidase) for building a nanobody array. Moreover, we used a nanobody-targeting enhanced green fluorescent protein (eGFP) as the model system to validate the protein immobilization method for building a nanobody array. Finally, by rapidly enriching eGFP, this method further highlights its potential for rapid diagnostic applications. This approach, characterized by its simplicity, high efficiency, and specificity, offers an advancement in the development of surface-modified protein arrays. It promises to enhance the sensitivity and accuracy of biomolecule detection, paving the way for broader applications in various research and diagnostic fields.

Unveiling the Halogenation-Induced Formation of Hg3Se2X2 (X = Cl, Br, and I) Compounds for Multiphase Mercury Cycling

The interaction between mercury (Hg) and inorganic compounds, including selenium (Se), sulfur (S), and halogens (X = Cl, Br, or I), plays a critical role in the global mercury cycle. However, most previously reported mercury compounds are susceptible to reduction, leading to the release of elemental mercury (Hg0) and causing secondary pollution. In this study, we unveil a groundbreaking discovery that underscores the vital role of halogenation in creating exceptionally stable Hg3Se2X2 compounds. Through the dynamic interplay of Hg, Se, and halogens, an intermediary stage denoted [HgSe]m[HgX2]n emerges, and this transformative process significantly elevates the stabilization of mercury. Remarkably, halogen ions strategically occupy pores at the periphery of HgSe clusters, engendering a more densely packed atomic arrangement of Hg, Se, and halogen components. A marked enhancement in both thermal and acid stability is observed, wherein temperatures ascend from 130 to 300 °C (transitioning from HgSe to Hg3Se2Cl2). This sequence of escalating stability follows the order HgSe < Hg3Se2I2 < Hg3Se2Br2 < Hg3Se2Cl2 for thermal resilience, complemented by virtually absent acid leaching. This innovative compound formation fundamentally alters the transformation pathways of gaseous Hg0 and ionic mercury (Hg2+), resulting in highly efficient in situ removal of both Hg0 and Hg2+ ions. These findings pave the way for groundbreaking advancements in mercury stabilization and environmental remediation strategies, offering a comprehensive solution through the creation of chemically stable precipitates.

Quantification of carboxylate-bridged di-zinc site stability in protein due ferri by single-molecule force spectroscopy

Carboxylate-bridged diiron proteins belong to a protein family involved in different physiological processes. These proteins share the conservative EXXH motif, which provides the carboxylate bridge and is critical for metal binding. Here, we choose de novo-designed single-chain due ferri protein (DFsc), a four-helical protein with two EXXH motifs as a model protein, to study the stability of the carboxylate-bridged di-metal binding site. The mechanical and kinetic properties of the di-Zn site in DFsc were obtained by atomic force microscopy-based single-molecule force spectroscopy. Zn-DFsc showed a considerable rupture force of ~200 pN, while the apo-protein is mechanically labile. In addition, multiple rupture pathways were observed with different probabilities, indicating the importance of the EXXH-based carboxylate-bridged metal site. These results demonstrate carboxylate-bridged di-metal site is mechanically stable and improve our understanding of this important type of metalloprotein.

Single Molecule Force Spectroscopy Studies on Metalloproteins: Opportunities and Challenges

Metalloproteins play important roles in a wide range of biological processes. Elucidating the mechanisms via which metalloproteins fold and constitute their metal centers is critical to the understanding of the functions and dynamics of metalloproteins. Owing to its superior force and length resolution, single-molecule force spectroscopy (SMFS) has evolved into a powerful tool to probe the unfolding and folding mechanisms of metalloproteins at the single level by forcing metalloproteins to unfold and then refold along a reaction coordinate defined by the applied stretching force. The folding of metalloproteins is complex and involves two interwound processes, the folding of the polypeptide chain and the constitution of the metal center. Experimental studies of the folding of metalloproteins are challenging. SMFS studies have allowed researchers to directly probe the folding and unfolding of metalloproteins at the single-molecule level and the effect of metal centers on the folding-unfolding energy landscape of metalloproteins. New mechanistic insights on the folding and unfolding of some metalloproteins have been obtained, demonstrating the power and unique advantages that SMFS techniques may offer. In this Perspective, using calcium-binding proteins and small iron-sulfur proteins as examples, I provide a concise overview of the information and insights that SMFS studies have provided to understand the folding and unfolding of metalloproteins. I also discuss the opportunities and challenges that are present in this fast-progressing area of research.