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Microbially derived peptides that mimic immunogenic gliadin peptides in celiac disease have been identified using a structure- and sequence-guided search. T cell activation assays and crystal structures reveal that a protein from the commensal bacterium Pseudomonas fluorescens can be processed and presented by antigen-presenting cells to potently activate T cells from patients with celiac disease.
A study reports the structures of membrane-bound flavin-containing monooxygenases (FMOs), solved using reconstructed ancestral mammalian FMOs. The models provide a structural basis for these enzymes’ mechanism of action and show how the proteins interact with membranes and how substrates access their active sites.
Bacterial T-boxes are regulatory mRNA regions that control the transcription or translation of factors involved in amino acid supply. T-boxes act by directly binding to non-aminoacylated tRNA in response to amino acid starvation. Three studies now capture three-dimensional structures of tRNA–T-box complexes and reveal a set of RNA features that are required for the recognition of specific tRNAs and modulation of gene expression.
Stabilization of the 3D genome architecture surrounding DNA lesions is critical for the maintenance of genome integrity. A new report by Ochs et al. shows how 53BP1 and RIF1 assemble a higher-order structure in the vicinity of damaged chromatin to protect it from unscheduled DNA-end resection.
Finally, the architecture of the translocase of the mitochondrial outer membrane (TOM complex) is revealed, after 20 years of anticipation. Two groups have now determined the near-atomic structures of the TOM complex. These findings improve understanding of the mechanisms by which TOM facilitates the passage of about 1,000 different proteins from the cytosol into the mitochondria.
Segmented, double-stranded RNA viruses of the Reoviridae family tightly regulate the activity of encapsidated polymerases to mediate the transition between genome replication and iterative rounds of multipartite transcription within a particle. By resolving multiple in situ structures of the transcribing complex, a new study reveals enzyme conformational changes and RNA trajectories during specific transcriptional states that support an ‘ouroboros’ model of conservative transcription for a member of the Reoviridae family.
Chromatin is compartmentalized spatially and temporally at multiple levels, but the precise organization of chromatin and mechanisms underlying its restructuring remain unclear. Two studies published in Cell and Nature now demonstrate the ability of chromatin to undergo liquid–liquid phase separation under physiological conditions and show that this intrinsic physicochemical property of chromatin can be regulated.
The first structure of this unusual recombinase in complex with substrate DNAs reveals surprisingly unpaired and refolded transposon end DNAs that are positioned in part by direct interactions with a GTP cofactor.
Tzelepis, Rausch and Kouzarides review the action of RNA modifications in the context of chromatin and discuss the emerging potential of RNA-modifying enzymes as new drug targets.
Arrowsmith and Schapira review recent progress in the discovery of drug-like small molecules that antagonize the function of non-bromodomain chromatin readers.
Upregulation of the X chromosome compensates for the presence of a single active X chromosome in mammals, but this has been difficult to measure and to understand mechanistically. A study now demonstrates that increased burst frequency boosts the transcriptional output of X-linked genes in male and female cells with a single active X chromosome. Interestingly, female embryonic stem cells lack increased burst frequency, which is established only after inactivation of the X chromosome takes place; this finding reveals a switch that can modulate transcriptional bursting.
Husmann and Gozani review the biochemical and biological activities of histone lysine methyltransferases and their connections to human diseases, focusing on cancer.
Zaware and Zhou review the current understanding of bromodomain biology and discuss the latest development of small-molecule inhibitors that target these protein domains as emerging therapies for cancer and inflammatory disorders.
A new cryo-EM structure of the bacterial flagellar hook, which connects the motor to the flagellar filament, reveals 11 distinctive conformations of the subunit. The cooperative dynamic switching among these states offers a dramatic extension of two-state models of protein allostery.
Beige fat serves as a substantial metabolic sink that dissipates energy and has consequently attracted much attention as a target for improving metabolic health. A recent study has provided a new molecular target, the N-terminal acetyltransferase Naa10p, for harnessing beige-fat biogenesis and improving whole-body energy homeostasis1.
The ‘N-end rule’ correlates the identity of the N-terminal residue of a protein to its in vivo half-life. A study has now shown that an N-terminal glycine can serve as a potent degradation signal, which reveals a novel branch of N terminus–dependent protein degradation.
Small RNAs guide nuclear Argonaute proteins to silence genomic target loci via recruitment of factors that lead to formation of repressive heterochromatin. Animal gonads use this pathway to repress transposable elements with PIWI-clade Argonaute proteins and their associated small RNAs called PIWI-interacting RNAs (piRNAs). Four research groups now identify a protein complex that acts as a molecular bridge between the piRNA pathway and the epigenetic silencing machinery.
Researchers have sought to understand the function and regulation of the motor protein dynein since its discovery more than 50 years ago1. Dynein-2 is one of the motors that move the intraflagellar transport (IFT) trains ― large protein complexes that are needed for the assembly and function of eukaryotic cilia and flagella. Toropova et al. report the single-particle cryo-EM structure of the human dynein-2 complex2, which unexpectedly reveals two different conformations of the motor subunit tails. One tail forms a zigzag that matches the periodicity of the IFT trains, which reinforces the auto-inhibition of dynein motor activity and the binding of multiple dynein-2 complexes along the train during anterograde transport.
This review proposes an up-to-date, consensus thermodynamic model for the conformational changes associated with transport by the eukaryotic type I exporters from the ABC family and discusses structural insights into ABC transporter pharmacology.
