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1. Point Mutations in TbpA Abrogate Human Transferrin Binding in Neisseria gonorrhoeae

   https://doi.org/10.1128/iai.00414-22  

   Greenawalt, Ashley Nicole; Stoudenmire, Julie; Lundquist, Karl; Noinaj, Nicholas; Gumbart, James C.; Cornelissen, Cynthia Nau (November 2022, Infection and Immunity)

   Bäumler, Andreas J. (Ed.)

   ABSTRACT TonB-dependent transporters (TDTs) are essential proteins for metal acquisition, an important step in the growth and pathogenesis of many pathogens, including Neisseria gonorrhoeae , the causative agent of gonorrhea. There is currently no available vaccine for gonorrhea; TDTs are being investigated as vaccine candidates because they are highly conserved and expressed in vivo . Transferrin binding protein A (TbpA) is an essential virulence factor in the initiation of experimental infection in human males and functions by acquiring iron upon binding to host transferrin (human transferrin [hTf]). The loop 3 helix (L3H) is a helix finger that inserts into the hTf C-lobe and is required for hTf binding and subsequent iron acquisition. This study identified and characterized the first TbpA single-point substitutions resulting in significantly decreased hTf binding and iron acquisition, suggesting that the helix structure is more important than charge for hTf binding and utilization. The tbpA D355P Δ tbpB and tbpA A356P Δ tbpB mutants demonstrated significantly reduced hTf binding and impaired iron uptake from Fe-loaded hTf; however, only the tbpA A356P Δ tbpB mutant was able to grow when hTf was the sole source of iron. The expression of tbpB was able to restore function in all tbpA mutants. These results implicate both D355 and A356 in the key binding, extraction, and uptake functions of gonococcal TbpA. 

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2. Nanopore Detection of Metal Ions: Current Status and Future Directions

   https://doi.org/10.1002/smtd.202000266  

   Roozbahani, Golbarg Mohammadi; Chen, Xiaohan; Zhang, Youwen; Wang, Liang; Guan, Xiyun (August 2020, Small Methods)

   Abstract In this review, recent research efforts that aimed at developing nanopore sensors for detection of metal ions, which play a crucial role in environmental safety and human health, are highlighted. Protein pores use three stochastic sensing‐based strategies for metal ion detection. The first strategy is to construct engineered nanopores with metal ion binding sites, so that the interaction between the target analytes and the nanopore can slow the movement of metal ions in the nanochannel. Second, large molecules such as nucleic acids and especially peptides can be utilized as external selective molecular probes to detect metal ions based on the conformational change of the ligand molecules induced by the metal ion–ligand chelation/coordination interaction. Third, enzymatic reactions can also be used as an alternative to the molecule probe strategy in the situation that a sensitive and selective probe molecule for the target analyte is difficult to obtain. On the other hand, by taking advantage of steady‐state analysis, synthetic nanopores mainly use two strategies (modification and modification‐free) to detect metals. Given the advantages of high sensitivity and selectivity, and label‐free detection, nanopore‐based metal ion sensors should find useful application in many fields, including environmental monitoring, medical diagnosis, and so on. 

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3. Phylogenetic and sequence analyses of insect transferrins suggest that only transferrin 1 has a role in iron homeostasis

   https://doi.org/10.1111/1744-7917.12783  

   Najera, Diana G.; Dittmer, Neal T.; Weber, Jacob J.; Kanost, Michael R.; Gorman, Maureen J. (June 2020, Insect Science)

   Abstract Iron is essential to life, but surprisingly little is known about how iron is managed in nonvertebrate animals. In mammals, the well‐characterizedtransferrinsbind iron and are involved in iron transport or immunity, whereas other members of thetransferrinfamily do not have a role in iron homeostasis. In insects, the functions oftransferrinsare still poorly understood. The goals of this project were to identify thetransferringenes in a diverse set of insect species, resolve the evolutionary relationships among these genes, and predict which of thetransferrinsare likely to have a role in iron homeostasis. Our phylogenetic analysis oftransferrinsfrom 16 orders of insects and two orders of noninsect hexapods demonstrated that there are four orthologous groups of insecttransferrins. Our analysis suggests thattransferrin 2arose prior to the origin of insects, andtransferrins 1,3, and4arose early in insect evolution. Primary sequence analysis of each of the insecttransferrinswas used to predict signal peptides, carboxyl‐terminal transmembrane regions, GPI‐anchors, and iron binding. Based on this analysis, we suggest thattransferrins 2,3, and4are unlikely to play a major role in iron homeostasis. In contrast, thetransferrin 1orthologs are predicted to be secreted, soluble, iron‐binding proteins. We conclude thattransferrin 1orthologs are the most likely to play an important role in iron homeostasis. Interestingly, it appears that the louse, aphid, and thrips lineages have lost thetransferrin 1gene and, thus, have evolved to manage iron withouttransferrins. 

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4. False negative and false positive free nanopore fabrication via adaptive learning of the controlled dielectric breakdown

   Rosha, Kamyar; Tang, Zifan; Guan, Weihua (May 2019, Transducer 2019)

   We investigate the current transport characteristics in the electrolyte-dielectric-electrolyte structure commonly used in the in-situ controlled breakdown (CBD) fabrication of solid-state nanopores. It is found that the stochastic breakdown process could lead to fidelity issues of false positives (an incorrect indication of a true nanopore formation) and false negatives (inability to detect initial nanopore formation). Robust and deterministic detection of initial physical breakdown to alleviate false positives and false negatives is critical for precise nanopore size control. To this end, we report a high fidelity moving Z-Score method based CBD fabrication of solid-state nanopore. We demonstrate 100% success rate of realizing the initial nanopore conductance of 3±1 nS (corresponds to the size of 1.7±0.6 nm) regardless of the dielectric membrane characteristics. Our study also elucidates the Joule heating is the dominant mechanism for electric field-based nanopore enlargement. Single DNA molecule sensing using nanopores fabricated by this method was successfully demonstrated. We anticipate the moving Z-Score based CBD method could enable broader access to the solid state nanopore-based single molecule analysis. 

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5. On the border between localization and delocalization: tris(iminoxolene)titanium( iv )

   https://doi.org/10.1039/C8DT04528C  

   Marshall-Roth, Travis; Yao, Kun; Parkhill, John A.; Brown, Seth N. (January 2019, Dalton Transactions)

   The tris(aminophenol) ligand tris(4-methyl-2-(3′,5′-di- tert -butyl-2′-hydroxyphenylamino)phenyl)amine, MeClampH 6 , reacts with Ti(O i Pr) 4 to give, after exposure to air, the dark purple, neutral, diamagnetic complex (MeClamp)Ti. The compound is six-coordinate, with an uncoordinated central nitrogen (Ti–N = 2.8274(12) Å), and contains titanium( iv ) and a doubly oxidized ligand, formally a bis(iminosemiquinone)-mono(amidophenoxide). The compound is unsymmetrical in the solid state, though the three ligands are equivalent on the NMR timescale in solution. Ab initio calculations indicate that the ground state is a multiconfigurational singlet, with a low-lying multiconfigurational triplet state. Variable-temperature NMR measurements are consistent with a singlet–triplet gap of 1200 ± 70 cm −1 , in good agreement with calculations. The distortion from threefold symmetry allows a low-lying, partially populated ligand-centered π nonbonding orbital to mix with largely occupied metal–ligand π bonding orbitals. The energetic accessibility of this distortion is inversely related to the strength of the metal–ligand π bonding interaction. 

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