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1. Association of the malate dehydrogenase-citrate synthase metabolon is modulated by intermediates of the Krebs tricarboxylic acid cycle

   https://doi.org/10.1038/s41598-021-98314-z  

   Omini, Joy; Wojciechowska, Izabela; Skirycz, Aleksandra; Moriyama, Hideaki; Obata, Toshihiro (September 2021, Scientific Reports)

   Abstract Mitochondrial malate dehydrogenase (MDH)-citrate synthase (CS) multi-enzyme complex is a part of the Krebs tricarboxylic acid (TCA) cycle ‘metabolon’ which is enzyme machinery catalyzing sequential reactions without diffusion of reaction intermediates into a bulk matrix. This complex is assumed to be a dynamic structure involved in the regulation of the cycle by enhancing metabolic flux. Microscale Thermophoresis analysis of the porcine heart MDH-CS complex revealed that substrates of the MDH and CS reactions, NAD⁺and acetyl-CoA, enhance complex association while products of the reactions, NADH and citrate, weaken the affinity of the complex. Oxaloacetate enhanced the interaction only when it was present together with acetyl-CoA. Structural modeling using published CS structures suggested that the binding of these substrates can stabilize the closed format of CS which favors the MDH-CS association. Two other TCA cycle intermediates, ATP, and low pH also enhanced the association of the complex. These results suggest that dynamic formation of the MDH-CS multi-enzyme complex is modulated by metabolic factors responding to respiratory metabolism, and it may function in the feedback regulation of the cycle and adjacent metabolic pathways. 

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2. The Protein-Protein Interaction Network Reveals a Novel Role of the Signal Transduction Protein PII in the Control of c-di-GMP Homeostasis in Azospirillum brasilense

   https://doi.org/10.1128/mSystems.00817-20  

   Gerhardt, Edileusa C.; Parize, Erick; Gravina, Fernanda; Pontes, Flávia L.; Santos, Adrian R.; Araújo, Gillize A.; Goedert, Ana C.; Urbanski, Alysson H.; Steffens, Maria B.; Chubatsu, Leda S.; et al (December 2020, mSystems)

   Porto, Carla (Ed.)

   ABSTRACT The PII family comprises a group of widely distributed signal transduction proteins ubiquitous in prokaryotes and in the chloroplasts of plants. PII proteins sense the levels of key metabolites ATP, ADP, and 2-oxoglutarate, which affect the PII protein structure and thereby the ability of PII to interact with a range of target proteins. Here, we performed multiple ligand fishing assays with the PII protein orthologue GlnZ from the plant growth-promoting nitrogen-fixing bacterium Azospirillum brasilense to identify 37 proteins that are likely to be part of the PII protein-protein interaction network. Among the PII targets identified were enzymes related to nitrogen and fatty acid metabolism, signaling, coenzyme synthesis, RNA catabolism, and transcription. Direct binary PII-target complex was confirmed for 15 protein complexes using pulldown assays with recombinant proteins. Untargeted metabolome analysis showed that PII is required for proper homeostasis of important metabolites. Two enzymes involved in c-di-GMP metabolism were among the identified PII targets. A PII-deficient strain showed reduced c-di-GMP levels and altered aerotaxis and flocculation behavior. These data support that PII acts as a major metabolic hub controlling important enzymes and the homeostasis of key metabolites such as c-di-GMP in response to the prevailing nutritional status. IMPORTANCE The PII proteins sense and integrate important metabolic signals which reflect the cellular nutrition and energy status. Such extraordinary ability was capitalized by nature in such a way that the various PII proteins regulate different facets of metabolism by controlling the activity of a range of target proteins by protein-protein interactions. Here, we determined the PII protein interaction network in the plant growth-promoting nitrogen-fixing bacterium Azospirillum brasilense . The interactome data along with metabolome analysis suggest that PII functions as a master metabolic regulator hub. We provide evidence that PII proteins act to regulate c-di-GMP levels in vivo and cell motility and adherence behaviors. 

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3. The mechanism of β- N -methylamino-l-alanine inhibition of tRNA aminoacylation and its impact on misincorporation

   https://doi.org/10.1074/jbc.RA119.011714  

   Han, Nien-Ching; Bullwinkle, Tammy J.; Loeb, Kaeli F.; Faull, Kym F.; Mohler, Kyle; Rinehart, Jesse; Ibba, Michael (January 2020, Journal of Biological Chemistry)

   β- N -methylamino- l -alanine (BMAA) is a nonproteinogenic amino acid that has been associated with neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and Alzheimer's disease (AD). BMAA has been found in human protein extracts; however, the mechanism by which it enters the proteome is still unclear. It has been suggested that BMAA is misincorporated at serine codons during protein synthesis, but direct evidence of its cotranslational incorporation is currently lacking. Here, using LC-MS–purified BMAA and several biochemical assays, we sought to determine whether any aminoacyl-tRNA synthetase (aaRS) utilizes BMAA as a substrate for aminoacylation. Despite BMAA's previously predicted misincorporation at serine codons, following a screen for amino acid activation in ATP/PP i exchange assays, we observed that BMAA is not a substrate for human seryl-tRNA synthetase (SerRS). Instead, we observed that BMAA is a substrate for human alanyl-tRNA synthetase (AlaRS) and can form BMAA-tRNA Ala by escaping from the intrinsic AlaRS proofreading activity. Furthermore, we found that BMAA inhibits both the cognate amino acid activation and the editing functions of AlaRS. Our results reveal that, in addition to being misincorporated during translation, BMAA may be able to disrupt the integrity of protein synthesis through multiple different mechanisms. 

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4. Hox proteins interact to pattern neuronal subtypes in Caenorhabditis elegans males

   https://doi.org/10.1093/genetics/iyac010  

   Kalis, Andrea K; Sterrett, Maria C; Armstrong, Cecily; Ballmer, Amarantha; Burkstrand, Kylie; Chilson, Elizabeth; Emlen, Estee; Ferrer, Emma; Loeb, Seanna; Olin, Taylor; et al (February 2022, Genetics)

   Hobert, O (Ed.)

   Abstract Hox transcription factors are conserved regulators of neuronal subtype specification on the anteroposterior axis in animals, with disruption of Hox gene expression leading to homeotic transformations of neuronal identities. We have taken advantage of an unusual mutation in the Caenorhabditis elegans Hox gene lin-39, lin-39(ccc16), which transforms neuronal fates in the C. elegans male ventral nerve cord in a manner that depends on a second Hox gene, mab-5. We have performed a genetic analysis centered around this homeotic allele of lin-39 in conjunction with reporters for neuronal target genes and protein interaction assays to explore how LIN-39 and MAB-5 exert both flexibility and specificity in target regulation. We identify cis-regulatory modules in neuronal reporters that are both region-specific and Hox-responsive. Using these reporters of neuronal subtype, we also find that the lin-39(ccc16) mutation disrupts neuronal fates specifically in the region where lin-39 and mab-5 are coexpressed, and that the protein encoded by lin-39(ccc16) is active only in the absence of mab-5. Moreover, the fates of neurons typical to the region of lin-39-mab-5 coexpression depend on both Hox genes. Our genetic analysis, along with evidence from Bimolecular Fluorescence Complementation protein interaction assays, supports a model in which LIN-39 and MAB-5 act at an array of cis-regulatory modules to cooperatively activate and to individually activate or repress neuronal gene expression, resulting in regionally specific neuronal fates. 

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5. Teaching virtual protein‐centric CUREs and UREs using computational tools

   Bell, Anthony. (September 2020, Biochemistry and molecular biology education)

   Responding to the need to teach remotely due to COVID-19, we used readily available computational approaches (and developed associated tutorials (https://mdh-cures-community.squarespace.com/virtual-cures-and-ures)) to teach virtual Course-Based Undergraduate Research Experience (CURE) laboratories that fulfil generally accepted main components of CUREs or Undergraduate Research Experiences (UREs): Scientific Background, Hypothesis Development, Proposal, Experiments, Teamwork, Data Analysis, Conclusions, and Presentation1. We then developed and taught remotely, in three phases, protein-centric CURE activities that are adaptable to virtually any protein, emphasizing contributions of noncovalent interactions to structure, binding and catalysis (an ASBMB learning framework2 foundational concept). The courses had five learning goals (unchanged in the virtual format),focused on i) use of primary literature and bioinformatics, ii) the roles of non-covalent interactions, iii) keeping accurate laboratory notebooks, iv) hypothesis development and research proposal writing, and, v) presenting the project and drawing evidence based conclusions The first phase, Developing a Research Proposal, contains three modules, and develops hallmarks of a good student-developed hypothesis using available literature (PubMed3) and preliminary observations obtained using bioinformatics, Module 1: Using Primary Literature and Data Bases (Protein Data Base4, Blast5 and Clustal Omega6), Module 2: Molecular Visualization (PyMol7 and Chimera8), culminating in a research proposal (Module 3). Provided rubrics guide student expectations. In the second phase, Preparing the Proteins, students prepared necessary proteins and mutants using Module 4: Creating and Validating Models, which leads users through creating mutants with PyMol, homology modeling with Phyre29 or Missense10, energy minimization using RefineD11 or ModRefiner12, and structure validation using MolProbity13. In the third phase, Computational Experimental Approaches to Explore the Questions developed from the Hypothesis, students selected appropriate tools to perform their experiments, chosen from computational techniques suitable for a CURE laboratory class taught remotely. Questions, paired with computational approaches were selected from Modules 5: Exploring Titratable Groups in a Protein using H++14, 6: Exploring Small Molecule Ligand Binding (with SwissDock15), 7: Exploring Protein-Protein Interaction (with HawkDock16), 8: Detecting and Exploring Potential Binding Sites on a Protein (with POCASA17 and SwissDock), and 9: Structure-Activity Relationships of Ligand Binding & Drug Design (with SwissDock, Open Eye18 or the Molecular Operating Environment (MOE)19). All involve freely available computational approaches on publicly accessible web-based servers around the world (with the exception of MOE). Original literature/Journal club activities on approaches helped students suggest tie-ins to wet lab experiments they could conduct in the future to complement their computational approaches. This approach allowed us to continue using high impact CURE teaching, without changing our course learning goals. Quantitative data (including replicates) was collected and analyzed during regular class periods. Students developed evidence-based conclusions and related them to their research questions and hypotheses. Projects culminated in a presentation where faculty feedback was facilitated with the Virtual Presentation platform from QUBES20 These computational approaches are readily adaptable for topics accessible for first to senior year classes and individual research projects (UREs). We used them in both partial and full semester CUREs in various institutional settings. We believe this format can benefit faculty and students from a wide variety of teaching institutions under conditions where remote teaching is necessary. 

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