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1. Probing the Ni ²⁺ ‐selective Response of Fluorescent Probe NiSensor‐1 with the NiCast Photocaged Complex ^{† ‡}

   https://doi.org/10.1111/php.13567  

   Hickey, Erin E.; Kennedy, Daniel P.; Gwizdala, Celina; Basa, Prem N.; Müller, Peter; MacDonald, John; Burdette, Shawn C. (December 2021, Photochemistry and Photobiology)

   Abstract CTEA (N,N‐bis[2‐(carboxylmethyl)thioethyl]amine) is a mixed donor ligand that has been incorporated into multiple fluorescent sensors such as NiSensor‐1 that was reported to be selective for Ni²⁺. Other metal ions such as Zn²⁺do not produce an emission response in aqueous solution. To investigate the coordination chemistry and selectivity of this receptor, we prepared NiCast, a photocage containing the CTEA receptor. Cast photocages undergo a photoreaction that decreases electron density on a metal‐bound aniline nitrogen atom, which shifts the binding equilibrium toward unbound metal ion. The unique selectivity of CTEA was examined by measuring the binding affinity of NiCast and the CTEA receptor for Ni²⁺, Zn²⁺, Cd²⁺and Cu²⁺under different conditions. In aqueous solution, Ni²⁺binds more strongly to the aniline nitrogen atom than Cd²⁺; however, in CH₃CN, the change in affinity virtually disappears. The crystal structure of [Cu(CTEA)], which exhibits a Jahn–Teller–distorted square pyramidal structure, was also analyzed to gain more insight into the underlying coordination chemistry. These studies suggest that the fluorescence selectivity of NiSensor‐1 in aqueous solution is due to a stronger interaction between the aniline nitrogen atom and Ni²⁺compared to other divalent metal ions except Cu²⁺. 

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2. Long-range dynamic correlations regulate the catalytic activity of the bacterial tyrosine kinase Wzc

   https://doi.org/10.1126/sciadv.abd3718  

   Hajredini, Fatlum; Piserchio, Andrea; Ghose, Ranajeet (December 2020, Science Advances)

   null (Ed.)

   BY-kinases represent a highly conserved family of protein tyrosine kinases unique to bacteria without eukaryotic orthologs. BY-kinases are regulated by oligomerization-enabled transphosphorylation on a C-terminal tyrosine cluster through a process with sparse mechanistic detail. Using the catalytic domain (CD) of the archetypal BY-kinase, Escherichia coli Wzc, and enhanced-sampling molecular dynamics simulations, isothermal titration calorimetry and nuclear magnetic resonance measurements, we propose a mechanism for its activation and nucleotide exchange. We find that the monomeric Wzc CD preferentially populates states characterized by distortions at its oligomerization interfaces and by catalytic element conformations that allow high-affinity interactions with ADP but not with ATP·Mg 2+ . We propose that oligomer formation stabilizes the intermonomer interfaces and results in catalytic element conformations suitable for optimally engaging ATP·Mg 2+ , facilitating exchange with bound ADP. This sequence of events, oligomerization, i.e., substrate binding, before engaging ATP·Mg 2+ , facilitates optimal autophosphorylation by preventing a futile cycle of ATP hydrolysis. 

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3. Laser-cooling Cadmium Bosons and Fermions with Near Ultraviolet Triplet Excitations

   https://doi.org/10.1088/1742-6596/2889/1/012006  

   Gibble, Kurt (November 2024, Journal of Physics: Conference Series)

   Abstract Cadmium is laser-cooled and trapped with excitations to triplet states with UVA light, first using only the 67 kHz wide 326 nm intercombination line and subsequently, for large loading rates, the 25 MHz wide 361 nm³P₂→³D₃transition. Eschewing the hard UV 229 nm¹S₀→¹P₁transition, only small magnetic fields gradients, less than 6 G cm⁻¹, are required enabling a 100% transfer of atoms from the 361 nm trap to the 326 nm narrow-line trap. All 8 stable cadmium isotopes are straightforwardly trapped, including two nuclear-spin- $\frac{1}{2}$fermions that require no additional repumping. We observe evidence of³P₂collisions limiting the number of trapped metastable atoms, report isotope shifts for¹¹¹Cd and¹¹³Cd of the 326 nm¹S₀→³P₁, 480nm³P₁→³S₁, and 361 nm³P₂→³D₃transitions, and measure the¹¹⁴Cd 5s5p³P₂→ 5s5d³D₃transition frequency to be 830 096 573(15) MHz. 

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4. Gelsolin-mediated actin filament severing, mechanics, and conformational changes at neutral and acidic pH

   https://doi.org/10.3389/frsfm.2025.1530439  

   Douglas, Taylor V; Toland, Claire A; Paulin, Sydney A; Castaneda, Nicholas; Tetard, Laurene; Kang, Ellen H (March 2025, Frontiers in Soft Matter)

   Gelsolin is a calcium (Ca²⁺) dependent, pH sensitive actin-binding protein that regulates actin filament dynamics to remodel the actin cytoskeleton. It is known that gelsolin binding induces conformational changes of actin filaments, leading to filament severing. However, the influence of physiological conditions, such as pH variations, on gelsolin-mediated filament severing activities, mechanics and conformations remains unclear despite their role in actin-actin interactions. Using Total Internal Reflection Fluorescence (TIRF) microscopy imaging and pyrene fluorescence assays, we demonstrate that filament severing efficiencies by gelsolin are enhanced in acidic conditions. In addition, analysis of filament thermal fluctuations using TIRF reveals that gelsolin binding stiffens actin filaments. Furthermore, we show that gelsolin binding induces conformational changes in filaments by measuring the filament half-pitch using high resolution Atomic Force Microscopy imaging. Together, our results suggest that pH modulation plays a key role in gelsolin-mediated filament severing activities, bending mechanics, and conformational changes, which have implications in many cellular processes including cell motility and morphogenesis. 

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5. Spectroscopic and metal binding properties of a de novo metalloprotein binding a tetrazinc cluster

   https://doi.org/10.1002/bip.23229  

   Chino, Marco; Zhang, Shao‐Qing; Pirro, Fabio; Leone, Linda; Maglio, Ornella; Lombardi, Angela; DeGrado, William F. (September 2018, Biopolymers)

   Abstract De novodesign provides an attractive approach, which allows one to test and refine the principles guiding metalloproteins in defining the geometry and reactivity of their metal ion cofactors. Although impressive progress has been made in designing proteins that bind transition metal ions including iron–sulfur clusters, the design of tetranuclear clusters with oxygen‐rich environments remains in its infancy. In previous work, we described the design of homotetrameric four‐helix bundles that bind tetra‐Zn²⁺clusters. The crystal structures of the helical proteins were in good agreement with the overall design, and the metal‐binding and conformational properties of the helical bundles in solution were consistent with the crystal structures. However, the correspondingapo‐proteins were not fully folded in solution. In this work, we design three peptides, based on the crystal structure of the original bundles. One of the peptides forms tetramers in aqueous solution in the absence of metal ions as assessed by CD and NMR. It also binds Zn²⁺in the intended stoichiometry. These studies strongly suggest that the desired structure has been achieved in theapostate, providing evidence that the peptide is able to actively impart the designed geometry to the metal cluster. 

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