Editorial: The Influence of Metal Ions and their Complexes on the Function and Structure of Biological Macromolecules

Miroslaw Gilski ¹ Mannar R. Maurya ² Boguslaw Nocek ³ Krzysztof Brzezinski ^4*

• ¹ Faculty of Chemistry, Adam Mickiewicz University, Poznań, Greater Poland, Poland
• ² Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand, India
• ³ to be confirmed, Indianapolis, United States
• ⁴ Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznań, Poland

This special issue describes diverse studies on interactions between macromolecules and metal ions or their complexes, ranging from methodological aspects relevant to such research to structural and biochemical analyses of protein-metal ion complexes. The collection includes five original research studies and two review articles.Single-molecule techniques have revolutionized biophysical measurements, simplifying experiments significantly and allowing their performance with very low sample requirements. These techniques can characterize all types of biological macromolecules, including proteins, DNA and RNA. However, studies on macromolecules that bind metal cations are limited due to numerous limitations and obstacles. In their review, de la Torre and Pomorski focused on singlemolecule methods, such as single-molecule FRET, nanopores and optical tweezers, that could be applied to study macromolecules that bind metal cations. In particular, they discussed potential promises and difficulties that could be experienced during single-molecule measurements.Structural biology is a powerful tool for determining the three-dimensional structure of macromolecules of interest at atomic or nearly atomic resolution. It allows for visualizing macromolecule interactions with bound ligands, including metal cations. However, interpreting structural data is not always straightforward and obvious. The review by Majorek et al. highlights issues related to the limitations of structural methods and erroneous interpretation of experimental data, which might lead to misinterpretations of the metal's role and function within the macromolecule. In particular, the authors highlight various aspects of structural data available for metal cation-protein complexes and examine the quality of modeling metal ion binding sites across different structure determination methods.The research by Canyelles i Font et al. underlines an issue related to biologically and environmentally ubiquitous metal cations in the context of affecting high-throughput screening (HTS) enzyme-based assays. Indeed, contamination of chemical libraries, buffers, biological samples etc., with cations that interfere with assay components might generate significant errors and lead to incorrect conclusions. The authors tested three luciferase variants commonly used in bioluminescent HTS assays and analyzed the impact of metal ions on luciferase-mediated bioluminescence. The study indicated significant quenching effects within biologically and environmentally relevant concentration ranges of metal ions, indicating a substantial influence on HTS assays and the subsequent interpretation of experimental data. Based on the results obtained, the authors proposed a series of strategies that would allow selecting and modifying an assay best suited to the type of metal cation contamination.Ruthenium complexes are considered diagnostic and therapeutic agents that target a variety of protein The study by Oszajca et al. presents crystallographic and physicochemical analyses of several Ru(III) complexes-hen-egg white lysozyme adducts. The obtained results provide insights into the structure and stability of the adducts, giving hints on how the nature of N-heterocyclic ligands and hydrolytic behavior influence the binding of Ru(III) complexes to proteins.Finally, three original studies describe the biochemical and structural research of bacterial enzymes in the context of the role of zinc ions in catalysis. The research by Kelley et al. describes structural and biochemical studies of N α -acetyl-L-ornithine deacetylase from Escherichia coli, a promising antibiotic drug target. Herein, the authors report two crystal structures of this enzyme containing one or two zinc ions coordinated within the active site area. Two publications from Mariusz Jaskolski's group focus mainly on interactions of bacterial L-asparaginases from Rhizobium etli with zinc ions. The research by Sliwiak et al. showed that two L-asparaginase isoforms, ReAIV and ReAV, have different biochemical characteristics, complementing these forms in distinct environmental and physiological conditions. In particular, these two isoforms reveal a different response to various transition metal cations, including zinc. Finally, structural and biochemical studies of ReAV, as well as a mutagenic analysis of this enzyme described by Pokrywka et al., suggest the role of zinc cations in ReAV activity.The original research and review articles published in this Special Issue offered insights into the current bioinorganic chemistry, notably presented from various perspectives. Obviously, structural studies of biological macromolecule complexes with metal cations are of key importance for bioinorganic research. On the other hand, there is still room for developing other biophysical methods that could be applied to analyze the influence of metal ions and their complexes on the function and structure of biological macromolecules. We hope this collection will stimulate further research, advancing our understanding of macromolecule-metal cation interactions and their implications for human health and disease.