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The phospholipid transacylase tafazzin selects lipid substrates on the basis of the physical properties of the membrane domains in which it is active, preferring lipids in the inverted hexagonal phase, representing curved or hemifused membrane zones. This concept of segregation of activity is captured as a polarizing microscope image of a cooling liquid crystal emerging from an isotropic melt, which reveals a dark phase where there is no spatial arrangement of the molecules and periodic stripes in the liquid crystal regions where molecules tend to be parallel to each other, forming helices. Cover art by MaryLou Quillen, based on an image from Bohdan Senyuk and Oleg D. Lavrentovich. Article, p862
Ivano Bertini left us on 7 July after a short illness. The chemical, biological and biomedical communities—indeed, society at large—have lost a unique and magnetic personality that will not be easily forgotten by those who have known him personally.
By incorporating sequence homology and context associations, global probabilistic approaches to annotate genome-scale metabolic networks can substantially improve the accuracy of biochemical predictions, revealing potential functionality and directing experimental validation.
The phospholipid-lysophospholipid transacylase tafazzin is responsible for enrichment of the cardiolipin fraction of mitochondria with tetralinoleoyl-cardiolipin. The specificity for linoleoyl hydrocarbon chains is now explained by the specific action of tafazzin on negatively curved lipid monolayers.
Bacterial persisters consist of a phenotypic subpopulation that survives antibiotic treatment, prolonging infection. The GhoT toxin from the newly discovered ghoS-ghoT toxin-antitoxin system contributes to persistence, most likely by interfering with bacterial inner membrane integrity.
The mechanism for nitro group formation in the thaxtomin family of natural products is unknown. Genetic and biochemical studies now show the cytochrome P450 TxtE catalyzes this direct and regioselective nitration, using NO and O2 to modify a tryptophan indole ring.
DNA damage products influence DNA replication but also may induce stalling or mutagenesis during transcription. A competitive transcription and adduct bypass assay provides a new approach for assessing the transcriptional effects of DNA lesions and links transcriptional arrest of several lesions to nucleotide excision repair pathways.
The reconstitution of two fungal NRPSs provides the first biochemical evidence that these assembly lines use a condensation-like domain to complete the synthesis of cyclic natural products instead of the thioesterase domain used in bacterial species.
C18-ceramide mediates lethal autophagy by anchoring LC3B-II (lipidated LC3) to mitochondrial membranes during mitochondrial fission and thereby recruiting autophagosomes.
A small-molecule activator specific for PKM2 binds to a site distinct from the endogenous activator fructose-1,6-bisphosphate, promoting tetramerization and constitutive activation of PKM2, to inhibit xenograft tumor growth in mice.
A new global annotation strategy combines sequence identity and genomic context to provide probabilities for all metabolic assignments in a given species. Application of this method leads to multiple new annotations and validation of three enzymatic activities in B. subtilis.
Expanding the bacterial toxin-antitoxin system classes to a fifth class, GhoST was found to be involved in maintenance of persister cells, dormant cells that are tolerant of antibiotics. GhoS is the antitoxin, an endoribonuclease that cleaves the toxin mRNA ghoT, whose gene product is a membrane-lytic protein.
Tafazzin, the mitochondrial transacylase that is deficient in Barth syndrome, selects lipid substrates in the inverted hexagonal phase but does not react with bilayer lipids.