22nd international Biometals Webinars

The 22nd International BioMetals Webinars focused on metal homeostasis, specifically zinc and iron regulation, highlighting their critical roles in biological systems. The first presentation examined metallothioneins (MTs), cysteine-rich proteins essential for zinc buffering and homeostasis. Using biochemical, spectroscopic, and mass spectrometry techniques, the study revealed that human MT isoforms bind zinc with differentiated affinities rather than uniform picomolar affinity, identifying three distinct zinc-binding affinity groups. This polymorphism and metamorphism of MTs enable dynamic zinc buffering across a physiologically relevant range of labile zinc concentrations. Comparative analyses extended to MTs from animals, plants, and bacteria demonstrated conserved differentiated zinc-binding properties, suggesting a broad biological significance. Structural and proteomic approaches mapped zinc-binding sites and elucidated interdomain interactions critical for MT function. The second presentation addressed iron homeostasis in the opportunistic pathogen Pseudomonas aeruginosa, emphasizing the role of iron-regulated small RNAs (PrrF) in controlling iron-dependent metabolism and virulence. Experimental studies using flow-cell biofilms at physiologically relevant temperatures (37°C) demonstrated that PrrF is essential for biofilm formation under low-iron conditions, contrasting with previous findings at 25°C. PrrF-mediated repression of aminobenzoate degradation genes redirects anthranilate toward production of alkylquinolone quorum sensing molecules (AQs), which promote biofilm maturation via autolysis and extracellular DNA release. Additionally, pyochelin, a siderophore previously considered secondary, was shown to be crucial for iron acquisition and biofilm formation at 37°C, compensating for pyoverdine loss. These findings underscore temperature-dependent shifts in iron homeostasis mechanisms relevant to Pseudomonas pathogenicity. Together, these studies advance understanding of metal regulation in diverse biological contexts, with implications for metal-related cellular processes and microbial pathogenesis. introduction to the 22nd international Biometals Webinars The spotlights of these iBWs will be firstly on zinc binding comparisons to metallothioneins from various organisms. Metallothioneins aremetal-binding proteins essential in metallic stress conditions. The second spotlight will be on iron homeostasis in the opportunistic pathogen Pseudomonas aeruginosa.The focus will be on this homeostasis in bacterial biofims more resistant to antibiotherapy Polymorphism and metamorphism of metallothioneins in zinc homeostasis Artur Krężel is Professor of Biological Sciences and Department Chair of Chemical Biology at the University of Wrocław (Poland). He received his diploma in chemistry (master of science, 2000) and a Ph.D. degree in bioinorganic chemistry (2004) from the University of Wroclaw, Poland, under the supervision of Prof. Wojciech Bal. During his postdoctoral training (2004-2007) at the University of Texas Medical Branch in Galveston, he worked with Prof. Wolfgang Maret on mechanisms of cellular zinc homeostasis, which culminated in the discovery of metallothioneins as physiological zinc ion buffers. He then accepted a position as an assistant professor at the Faculty of Biotechnology of his alma mater. In 2011, he received a D.Sc. degree from his university. Currently, he is a full professor and head of the Department of Chemical Biology. His research concentrates on several areas at the interface of inorganic biochemistry, biophysics, and chemical biology, particularly understanding the molecular bases of zinc and copper metabolism. Examples of this endeavor are structure-function relationships, the stability of metalloproteins, protein folding and thermodynamics, and the development of new analytical methods, such as fluorescent probes for selective protein modifications and metal sensing, mass spectrometry approaches for studying metalloproteins (un)folding and structures. Iron homeostasis in Pseudomonas aeruginosa biofilms Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen that causes both acute and chronic infections in vulnerable populations. Treatment of P. aeruginosa infections is increasingly challenging due to multi-drug resistance, and biofilm formation during infection further increases antibiotic tolerance. Iron, which is sequestered by the host innate immune system, is also a key nutrient that is required for P. aeruginosa biofilm formation. The iron-responsive PrrF small regulatory RNAs (sRNAs) are key to P. aeruginosa’s iron starvation response, promote the production of the PQS quorum sensing molecule, and are required for virulence in murine lung infection. Prior work showed that the PrrF sRNAs are dispensable for biofilm formation; however, these studies were performed using flow-cell biofilms grown at room temperature. Here we demonstrate a temperature dependency for PrrF in P. aeruginosa biofilm formation: the genes for these sRNAs are required for optimal biofilm formation at 37°C but not 25°C. We further show that a ∆pqsA mutant, which lacks production of PQS and related metabolites, phenocopies the ∆prrF mutant. These studies demonstrate the importance of the PrrF sRNAs in P. aeruginosa biofilm formation at body temperature and reveal a previously under-appreciated role of temperature in iron homeostasis and P. aeruginosa biofilm physiology.