More Like this

1. Flexible B ₁₂ ecophysiology of Phaeocystis antarctica due to a fusion B ₁₂ –independent methionine synthase with widespread homologues

   https://doi.org/10.1073/pnas.2204075121  

   Rao, Deepa; Füssy, Zoltán; Brisbin, Margaret M; McIlvin, Matthew R; Moran, Dawn M; Allen, Andrew E; Follows, Michael J; Saito, Mak A (February 2024, Proceedings of the National Academy of Sciences)

   Coastal Antarctic marine ecosystems are significant in carbon cycling because of their intense seasonal phytoplankton blooms. Southern Ocean algae are primarily limited by light and iron (Fe) and can be co-limited by cobalamin (vitamin B₁₂). Micronutrient limitation controls productivity and shapes the composition of blooms which are typically dominated by either diatoms or the haptophytePhaeocystis antarctica. However, the vitamin requirements and ecophysiology of the keystone speciesP. antarcticaremain poorly characterized. Using cultures, physiological analysis, and comparative omics, we examined the response ofP. antarcticato a matrix of Fe-B₁₂conditions. We show thatP. antarcticais not auxotrophic for B₁₂, as previously suggested, and identify mechanisms underlying its B₁₂response in cultures of predominantly solitary and colonial cells. A combination of proteomics and proteogenomics reveals a B₁₂-independent methionine synthase fusion protein (MetE-fusion) that is expressed under vitamin limitation and interreplaced with the B₁₂-dependent isoform under replete conditions. Database searches return homologues of the MetE-fusion protein in multiplePhaeocystisspecies and in a wide range of marine microbes, including other photosynthetic eukaryotes with polymorphic life cycles as well as bacterioplankton. Furthermore, we find MetE-fusion homologues expressed in metaproteomic and metatranscriptomic field samples in polar and more geographically widespread regions. As climate change impacts micronutrient availability in the coastal Southern Ocean, our finding thatP. antarcticahas a flexible B₁₂metabolism has implications for its relative fitness compared to B₁₂-auxotrophic diatoms and for the detection of B₁₂-stress in a more diverse set of marine microbes. 

   more » « less
2. Non‐native Intramolecular Radical Cyclization Catalyzed by a B ₁₂ ‐Dependent Enzyme**

   https://doi.org/10.1002/anie.202312893  

   Li, Jianbin; Kumar, Amardeep; Lewis, Jared C. (November 2023, Angewandte Chemie International Edition)

   Abstract Despite the unique reactivity of vitamin B₁₂and its derivatives, B₁₂‐dependent enzymes remain underutilized in biocatalysis. In this study, we repurposed the B₁₂‐dependent transcription factor CarH to enable non‐native radical cyclization reactions. An engineered variant of this enzyme, CarH*, catalyzes the formation γ‐ and δ‐lactams through either redox‐neutral or reductive ring closure with marked enhancement of reactivity and selectivity relative to the free B₁₂cofactor. CarH* also catalyzes an unusual spirocyclization by dearomatization of pendant arenes to produce bicyclic 1,3‐diene products instead of 1,4‐dienes provided by existing methods. These results and associated mechanistic studies highlight the importance of protein scaffolds for controlling the reactivity of B₁₂and expanding the synthetic utility of B₁₂‐dependent enzymes. 

   more » « less
3. Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TESS and CHEOPS

   https://doi.org/10.1093/mnras/stae1152  

   Dholakia, Shishir; Palethorpe, Larissa; Venner, Alexander; Mortier, Annelies; Wilson, Thomas G; Huang, Chelsea X; Rice, Ken; Van Eylen, Vincent; Nabbie, Emma; Cloutier, Ryan; et al (May 2024, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors 42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory, as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of 12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy. 

   more » « less
4. Demonstration of 4.7 kV breakdown voltage in NiO/ β -Ga ₂ O ₃ vertical rectifiers

   https://doi.org/10.1063/5.0097564  

   Li, Jian-Sian; Chiang, Chao-Ching; Xia, Xinyi; Yoo, Timothy Jinsoo; Ren, Fan; Kim, Honggyu; Pearton, S. J. (July 2022, Applied Physics Letters)

   Vertical heterojunction NiO/β n-Ga 2 O/n + Ga 2 O 3 rectifiers employing NiO layer extension beyond the rectifying contact for edge termination exhibit breakdown voltages (V B ) up to 4.7 kV with a power figure-of-merits, V B 2 /R ON of 2 GW·cm −2 , where R ON is the on-state resistance (11.3 mΩ cm 2 ). Conventional rectifiers fabricated on the same wafers without NiO showed V B values of 840 V and a power figure-of-merit of 0.11 GW cm −2 . Optimization of the design of the two-layer NiO doping and thickness and also the extension beyond the rectifying contact by TCAD showed that the peak electric field at the edge of the rectifying contact could be significantly reduced. The leakage current density before breakdown was 144 mA/cm 2 , the forward current density was 0.8 kA/cm 2 at 12 V, and the turn-on voltage was in the range of 2.2–2.4 V compared to 0.8 V without NiO. Transmission electron microscopy showed sharp interfaces between NiO and epitaxial Ga 2 O 3 and a small amount of disorder from the sputtering process. 

   more » « less
5. Anions Formed by Perchlorofluorobenzenes C ₆ Cl _n F _6–n ( n = 0–6)

   https://doi.org/10.1021/acs.jpca.4c04359  

   Sommerfeld, Thomas (September 2024, The Journal of Physical Chemistry A)

   Anions formed by the perhalobenzene series C$$_6$$Cl$$_{n}$$F$$_{6-n}$$ ($n=0-6$) are studied computationally. All members of the series form both stable valence and stable non-valence anions. At the geometry of the neutral parents, only non-valence anions are bound, and the respective vertical electron affinities show values in the $20$ to $60$meV range. Valence anions show distorted non-planar structures, and one can distinguish two types of conformers. A-type conformers show puckered-ring structures and excess electrons delocalized over several C-Cl bonds [in case of C$$_6$$F$$_6^-$$, C-F bonds], while B-type conformers possess excess electrons essentially localized in a single C-Cl bond, which is accordingly strongly stretched and bent out-of-plane. For a specific anion, all conformers are close in energy (relative energies of less than $10$kJ/mol) and are connected by low-lying transition states. Accordingly, A-type and B-type conformers possess similar adiabatic electron affinities, however, their vertical detachment energies exhibit drastically different values, which should ease conformer distinction in photoelectron spectroscopy. 

   more » « less