More Like this

1. SAR11 bacteria have a high affinity and multifunctional glycine betaine transporter

   https://doi.org/10.1111/1462-2920.14649  

   Noell, Stephen E. ; Giovannoni, Stephen J. ( May 2019 , Environmental Microbiology)

   Marine bacterioplankton face stiff competition for limited nutrient resources. SAR11, a ubiquitous clade of very small and highly abundantAlphaproteobacteria, are known to devote much of their energy to synthesizing ATP‐binding cassette periplasmic proteins that bind substrates. We hypothesized that their small size and relatively large periplasmic space might enable them to outcompete other bacterioplankton for nutrients. Using uptake experiments with¹⁴C‐glycine betaine, we discovered that two strains of SAR11,CandidatusPelagibacter sp. HTCC7211 andCand. P. ubique HTCC1062, have extraordinarily high affinity for glycine betaine (GBT), with half‐saturation (K_s) values around 1 nM and specific affinity values between 8 and 14 L mg cell⁻¹ h⁻¹. Competitive inhibition studies indicated that the GBT transporters in these strains are multifunctional, transporting multiple substrates in addition to GBT. Both strains could use most of the transported compounds for metabolism and ATP production. Our findings indicate thatPelagibactercells are primarily responsible for the high affinity and multifunctional GBT uptake systems observed in seawater. Maximization of whole‐cell affinities may enable these organisms to compete effectively for nutrients during periods when the gross transport capacity of the heterotrophic plankton community exceeds the supply, depressing ambient concentrations.

    

   more » « less
2. Resolved Measurements of the CO-to-H 2 Conversion Factor in 37 Nearby Galaxies

   https://doi.org/10.3847/1538-4357/ad23ed  

   Chiang 江, I-Da 宜達 ; Sandstrom, Karin M. ; Chastenet, Jérémy ; Bolatto, Alberto D. ; Koch, Eric W. ; Leroy, Adam K. ; Sun 孙, Jiayi 嘉懿 ; Teng, Yu-Hsuan ; Williams, Thomas G. ( March 2024 , The Astrophysical Journal)

   We measure the CO-to-H₂conversion factor (α_CO) in 37 galaxies at 2 kpc resolution, using the dust surface density inferred from far-infrared emission as a tracer of the gas surface density and assuming a constant dust-to-metal ratio. In total, we have ∼790 and ∼610 independent measurements ofα_COfor CO (2–1) and (1–0), respectively. The mean values forα_{CO (2–1)}andα_{CO (1–0)}are${9.3}_{-5.4}^{+4.6}$and${4.2}_{-2.0}^{+1.9}{M}_{\odot }{\mathrm{pc}}^{-2}{(\mathrm{K}\mathrm{km}{\mathrm{s}}^{-1})}^{-1}$, respectively. The CO-intensity-weighted mean is 5.69 forα_{CO (2–1)}and 3.33 forα_{CO (1–0)}. We examine howα_COscales with several physical quantities, e.g., the star formation rate (SFR), stellar mass, and dust-mass-weighted average interstellar radiation field strength ($\overline{U}$). Among them,$\overline{U}$, Σ_SFR, and the integrated CO intensity (W_CO) have the strongest anticorrelation with spatially resolvedα_CO. We provide linear regression results toα_COfor all quantities tested. At galaxy-integrated scales, we observe significant correlations betweenα_COandW_CO, metallicity,$\overline{U}$, and Σ_SFR. We also find thatα_COin each galaxy decreases with the stellar mass surface density (Σ_⋆) in high-surface-density regions (Σ_⋆≥ 100M_⊙pc⁻²), following the power-law relations${\alpha }_{\mathrm{CO}(2–1)}\propto {\mathrm{\Sigma }}_{\star }^{-0.5}$and${\alpha }_{\mathrm{CO}(1–0)}\propto {\mathrm{\Sigma }}_{\star }^{-0.2}$. The power-law index is insensitive to the assumed dust-to-metal ratio. We interpret the decrease inα_COwith increasing Σ_⋆as a result of higher velocity dispersion compared to isolated, self-gravitating clouds due to the additional gravitational force from stellar sources, which leads to the reduction inα_CO. The decrease inα_COat high Σ_⋆is important for accurately assessing molecular gas content and star formation efficiency in the centers of galaxies, which bridge “Milky Way–like” to “starburst-like” conversion factors.

    

   more » « less
3. 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)

   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⁺.

    

   more » « less
4. Structure and function of LCI1: a plasma membrane CO 2 channel in the Chlamydomonas CO 2 concentrating mechanism

   https://doi.org/10.1111/tpj.14745  

   Kono, Alfredo ; Chou, Tsung‐Han ; Radhakrishnan, Abhijith ; Bolla, Jani Reddy ; Sankar, Kannan ; Shome, Sayane ; Su, Chih‐Chia ; Jernigan, Robert L. ; Robinson, Carol V. ; Yu, Edward W. ; et al ( April 2020 , The Plant Journal)

   Microalgae and cyanobacteria contribute roughly half of the global photosynthetic carbon assimilation. Faced with limited access to CO₂in aquatic environments, which can vary daily or hourly, these microorganisms have evolved use of an efficient CO₂concentrating mechanism (CCM) to accumulate high internal concentrations of inorganic carbon (C_i) to maintain photosynthetic performance. For eukaryotic algae, a combination of molecular, genetic and physiological studies using the model organismChlamydomonas reinhardtii, have revealed the function and molecular characteristics of many CCM components, including active C_iuptake systems. Fundamental to eukaryotic C_iuptake systems are C_itransporters/channels located in membranes of various cell compartments, which together facilitate the movement of C_ifrom the environment into the chloroplast, where primary CO₂assimilation occurs. Two putative plasma membrane C_itransporters, HLA3 and LCI1, are reportedly involved in active C_iuptake. Based on previous studies, HLA3 clearly plays a meaningful role in HCO₃⁻transport, but the function of LCI1 has not yet been thoroughly investigated so remains somewhat obscure. Here we report a crystal structure of the full‐length LCI1 membrane protein to reveal LCI1 structural characteristics, as well asin vivophysiological studies in an LCI1 loss‐of‐function mutant to reveal the C_ispecies preference for LCI1. Together, these new studies demonstrate LCI1 plays an important role in active CO₂uptake and that LCI1 likely functions as a plasma membrane CO₂channel, possibly a gated channel.

    

   more » « less
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)

   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.

    

   more » « less