7,423 research outputs found
Radical S-adenosylmethionine enzymes: mechanism, control and function
No full textThe radical SAM superfamily of enzymes use an iron sulfur cluster to reduce S-adenosylmethionine, which leads to the formation of a highly reactive intermediate, usually the 50-deoxyadenosyl radical. This potent oxidant is able to functionalize relatively inert substrates, including unactivated C–H bonds. This reactivity is evidently useful, as radical SAM enzymes are widely distributed throughout metabolism and catalyze some of the most complex and elegant biotransformations. In the first part of this review, the focus is on the mechanism of radical formation, including the features shared across the family, followed by a discussion of recent evidence for variations in cluster binding motifs and the mechanism of radical formation. In the second part, we survey how radical SAM chemistry has been applied to biosynthesis
High-level expression and reconstitution of active Cfr, a radical-SAM rRNA methyltransferase that confers resistance to ribosome-acting antibiotics
No full textCfr is a radical-SAM (S-adenosyl-l-methionine) enzyme that methylates the 8 position of 23S rRNA residue A2503 to confer resistance to multiple antibiotic classes acting upon the large subunit of the bacterial ribosome. Radical-SAM enzymes use an Fe–S cluster to generate the 5?-deoxyadenosyl (DOA) radical from SAM, enabling them to modify intrinsically unreactive centres such as adenosine C8. However, despite its mechanistic interest and clinical relevance, until recently Cfr remained little characterised. Accordingly we have used co-expression with the Azotobacter vinelandii isc operon, encoding genes responsible for Fe–S cluster biosynthesis, to express hexahistidine-tagged Cfr in Escherichia coli BL21Star, and purified the recombinant protein in a yield more than 20 times greater than has been previously reported. As aerobically purified, Cfr contains secondary structure, is monomeric in solution and has an absorbance spectrum suggestive of a 2Fe–2S cluster. After anaerobic purification a 4Fe–4S cluster is indicated, while on reconstitution with excess iron and sulphide a further increase in metal content suggests that an additional, most likely 4Fe–4S, cluster is formed. Acquisition of additional secondary structure under these conditions indicates that Fe–S clusters are of structural, as well as functional, importance to Cfr. In the presence of sodium dithionite reconstituted Cfr is both reducible and able to cleave SAM to 5?-deoxyadeonsine (DOA), demonstrating that the purified reconstituted enzyme has radical-SAM activity. Co-expression with isc proteins thus enables recombinant active Cfr to be obtained in yields that facilitate its future spectroscopic and structural characterisation.<br/
Authors on the Hill presents: Thomas R. Martin
No full textThomas R. Martin is the Jeremiah O’Connor Professor in Classics. As an undergraduate he studied abroad in Rome and earned his AB degree at Princeton University; as a graduate student he studied abroad in Athens and earned his PhD at Harvard University. He currently teaches courses on ancient Greek and Latin language and literature, Alexander the Great and Asia, and democracy and rhetoric. His scholarly publications concern a range of topics in ancient Greek and Latin historical authors and Greek and Roman history. Prof. Martin is also one of the founders of the online Perseus Project and the author of its overview of ancient Greek history. He has appeared in a number of video and recorded programs on ancient Greece and Rome. [See the list on pp. 11-12 in his current CV.] His most recent book is Phocion: Good Citizen in a Divided Democracy (Yale Univ. Press, 2024). Written for readers who are interested in the early development of democracy, but who are not specialists in ancient history, the book explores the lessons that we can today learn from thinking about the long and ultimately disastrous political career of the Athenian leader Phocion (ca. 402-318 BCE). Prof. Martin asks how and why Phocion initially became famous and influential among his fellow citizens at Athens, but then ended up being blamed and executed as a national traitor during the period of Athenians’ fall from being a leading international power and of the violent fracturing of their renowned “direct democracy.”https://crossworks.holycross.edu/aoth/1022/thumbnail.jp
Benefits of a Classification Scheme of Granitic Pegmatites Based on Petrogenetic Considerations.
No full textOral presentation-
Communicating author: Martin RF
WHY IS AMAZONITIC K-FELDSPAR AN EARMARK OF NYF-TYPE GRANITIC PEGMATITES?
No full textOral presentation- Communicating author: Martin R
Product inhibition in the radical S-adenosylmethionine family
No full textMembers of the radical S-adenosylmethionine (AdoMet) superfamily reductively cleave AdoMet to generate the highly reactive 5?-deoxyadenosyl radical (DOA) which initiates biological transformations by abstraction of a hydrogen atom. We demonstrate that three members of the family: biotin synthase (BioB), lipoyl synthase (LipA) and tyrosine lyase (ThiH) are inhibited in vitro by a combination of the products 5?-deoxyadenosine (DOA) and methionine. These results suggest the observed inhibition is a common feature of the radical AdoMet proteins that form DOA and methionine as products. Addition of 5?-methylthioadenosine/S-adenosylhomocysteine nucleosidase (MTAN) to BioB, LipA or ThiH activity assays removed the product inhibition by catalysing the hydrolysis of DOA and gave an increase in activity
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Corvids and Canines in George R. R. Martin?s A Song of Ice and Fire
No full textThe series, A Song of Ice and Fire by George R. R. Martin has become increasingly popular among readers even during a time when fantasy novels have decreased in popularity. This rise in readership and viewership (with the television series Game of Thrones), has effectively started several discussions about the methods and choices of the author in regards to the plot, symbols, and characters.
This paper will look at two characters within the novels, namely the corvids and the canines Martin uses as catalysts for furthering the plot and understanding the main characters. This paper examines the historical use of the two animals and their relationship with one another as well as how Martin uses them to engage with the reader
Thiamine biosynthesis in Escherichia coli: Identification of the intermediate and by-product derived from tyrosine
No full textIn anaerobic organisms such as E. coli the tyrosine lyase ThiH is essential for the biosynthesis of the thiazole moiety of the vitamin thiamine. ThiH is a member of the radical AdoMet family. The products formed by cleavage of tyrosine in vitro have been identified and suggest a radical-mediated cleavage resulting in p-cresol and dehydroglycine which is hydrolyzed to glyoxylate
Namelessness in the Works of George R. R. Martin and Ursula Le Guin
No full textThe thesis explores the significance and implications of namelessness in fantasy literature on the example of A Song of Ice and Fire by George R. R. Martin and the Earthsea series by Ursula Le Guin. The literary use of namelessness serves to develop characters, examine power structures, and challenge traditional notions of identity and belonging. The author uses various theoretical perspectives, including those of Josef Campbell, Carl Jung, Michel Foucault, Gérard Genette, Jane Bliss, and Lao Tzu to analyze the phenomenon. By drawing on these diverse perspectives and applying different methods of analysis, the thesis highlights the interdisciplinary nature of the study, drawing from theories in history, mythology, psychology, philosophy, and literary criticism
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