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1. Crystal structure of a short-chain dehydrogenase from Burkholderia cenocepacia J2315 in complex with NADP ⁺ and benzoic acid

   https://doi.org/10.1107/S2053230X24011282  

   Belfon, Kafi_K J; Beyer, Olive; Abendroth, Jan; Dranow, David M; Lorimer, Donald D; Abramov, Ariel; Latimore, Yazmine; Hamilton, Connor; Dawkins, Aniah; Hinojosa, Isabella; et al (December 2024, Acta Crystallographica Section F Structural Biology Communications)

   Asojo, O (Ed.)

   Burkholderia cenocepaciais an opportunistic human pathogen that can cause lethal infections in immunocompromised individuals, particularly those with cystic fibrosis. As such, there is a critical need to identify and characterize the structure and function of enzymes that participate in the metabolic pathways of this bacterium. Here, the high-resolution X-ray crystal structure of a short-chain dehydrogenase reductase (SDR) fromB. cenocepaciaJ2315 (BcSDR) in complex with the coenzyme NADP⁺and a benzoic acid ligand is presented. This protein has the conserved Rossmann fold of the SDR superfamily and the characteristic TGxxxGxG motif of the classical SDR subfamily. However, unlike classical SDRs, the active site of BcSDR has a leucine residue in place of the highly conserved and catalytically important tyrosine residue. Sequence analysis confirms that this leucine residue is conserved in this SDR across the Burkholderiales order. This suggests that BcSDR is more appropriately classified into the divergent SDR subfamily. In addition, this enzyme would necessarily employ a different enzyme mechanism to that proposed as a general mechanism for most SDRs. 

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2. Reaction Initiation in Enzyme Crystals by Diffusion of Substrate

   https://doi.org/10.3390/cryst10020116  

   Schmidt, Marius (February 2020, Crystals)

   Ever since the first structure of an enzyme, lysozyme, was solved, scientists have been eager to explore how these molecules perform their catalytic function. There has been an overwhelmingly large body of publications that report the X-ray structures of enzymes determined after substrate and ligand binding. None of them truly show the structures of an enzyme working freely through a sequence of events that range from the formation of the enzyme–substrate complex to the dissociation of the product. The technical difficulties were too severe. By 1969, Sluyterman and de Graaf had pointed out that there might be a way to start a reaction in an enzyme crystal by diffusion and following its catalytic cycle in its entirety with crystallographic methods. The crystal only has to be thin enough so that the diffusion is not rate limiting. Of course, the key questions are as follows: How thin should the crystal be? Will the existing X-ray sources be able to collect data from a thin enough crystal fast enough? This review shines light on these questions. 

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3. The Luminosity Phase Space of Galactic and Extragalactic X-Ray Transients Out to Intermediate Redshifts

   https://doi.org/10.3847/1538-4357/acf765  

   Polzin, Ava; Margutti, Raffaella; Coppejans, Deanne_L; Auchettl, Katie; Page, Kim_L; Vasilopoulos, Georgios; Bright, Joe_S; Esposito, Paolo; Williams, Peter_K_G; Mukai, Koji; et al (December 2023, The Astrophysical Journal)

   Abstract We present a detailed compilation and analysis of the X-ray phase space of low- to intermediate-redshift (0 ≤z≤ 1) transients that consolidates observed light curves (and theory where necessary) for a large variety of classes of transient/variable phenomena in the 0.3–10 keV energy band. We include gamma-ray burst afterglows, supernovae, supernova shock breakouts and shocks interacting with the environment, tidal disruption events and active galactic nuclei, fast blue optical transients, cataclysmic variables, magnetar flares/outbursts and fast radio bursts, cool stellar flares, X-ray binary outbursts, and ultraluminous X-ray sources. Our overarching goal is to offer a comprehensive resource for the examination of these ephemeral events, extending the X-ray duration–luminosity phase space (DLPS) to show luminosity evolution. We use existing observations (both targeted and serendipitous) to characterize the behavior of various transient/variable populations. Contextualizing transient signals in the larger DLPS serves two primary purposes: to identify areas of interest (i.e., regions in the parameter space where one would expect detections, but in which observations have historically been lacking), and to provide initial qualitative guidance in classifying newly discovered transient signals. We find that while the most luminous (largely extragalactic) and least luminous (largely Galactic) part of the phase space is well populated att> 0.1 days, intermediate-luminosity phenomena (L_X= 10³⁴–10⁴²erg s⁻¹) represent a gap in the phase space. We thus identifyL_X= 10³⁴–10⁴²erg s⁻¹andt= 10⁻⁴to 0.1 days as a key discovery phase space in transient X-ray astronomy. 

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4. Structural insights into binding of polyglutamylated tetrahydrofolate by serine hydroxymethyltransferase 8 from soybean

   https://doi.org/10.3389/fpls.2024.1451839  

   Owuocha, Luckio F; Mitchum, Melissa G; Beamer, Lesa J (August 2024, Frontiers in Plant Science)

   Tetrahydrofolate and its derivatives participate in one-carbon transfer reactions in all organisms. The cellular form of tetrahydrofolate (THF) is modified by multiple glutamate residues and polyglutamylation plays a key role in organellar and cellular folate homeostasis. In addition, polyglutamylation of THF is known to increase the binding affinity to enzymes in the folate cycle, many of which can utilize polyglutamylated THF as a substrate. Here, we use X-ray crystallography to provide a high-resolution view of interactions between the enzyme serine hydroxymethyltransferase (SHMT), which provides one carbon precursors for the folate cycle, and a polyglutamylated form of THF. Our 1.7 Å crystal structure of soybean SHMT8 in complex with diglutamylated 5-formyl-THF reveals, for the first time, a structural rearrangement of a loop at the entrance to the folate binding site accompanied by the formation of novel specific interactions between the enzyme and the diglutamyl tail of the ligand. Biochemical assays show that additional glutamate moieties on the folate ligand increase both enzyme stability and binding affinity. Together these studies provide new information on SHMT structure and function and inform the design of anti-folate agents. 

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5. Multiwavelength Study of HESS J0632+057: New Insights into Pulsar–Disk Interaction

   https://doi.org/10.3847/1538-4357/adf6b6  

   Park, Jaegeun; An, Hongjun; Kim, Chanho; Matchett, Natalie; Mori, Kaya; van_Soelen, Brian; Archer, A; Bangale, P; Bartkoske, J T; Benbow, W; et al (September 2025, The Astrophysical Journal)

   Abstract We present an analysis of new multiwavelength observations of the TeV gamma-ray binary HESS J0632+057, conducted using SALT, Swift, NuSTAR, and VERITAS in 2023–2024. By combining these new data with archival observations, we confirm previous suggestions of orbital variability in the source’s X-ray spectrum, including increased X-ray absorption at the orbital phase interval ofϕ ≈ 0.3–0.4. The source’s X-ray flux within this phase interval seems to have exhibited a significant change on an orbital timescale. Additionally, occasional short-term variations in the X-ray band on a timescale of less than 3 days have been observed. The measured duration of the increased absorbing column density and the flux variability timescales can provide clues about the interaction between the putative pulsar and the Be companion’s disk if, as previously suggested, the pulsar crosses the disk at this phase interval. Moreover, the new contemporaneous X-ray and TeV observations around the pulsar-crossing phases revealed independent variability in the X-ray and TeV fluxes, contrary to a previous observation of concurrent flux increases. While these observations alone cannot provide definitive conclusions, we discuss our results in the context of pulsar–disk interaction and intrabinary shock emission scenarios. 

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