Extrinsic stabilization of antiviral ACE2-Fc fusion proteins targeting SARS-CoV-2.

The angiotensin-converting enzyme 2 (ACE2) is a viral receptor used by sarbecoviruses to infect cells. Fusion proteins comprising extracellular ACE2 domains and the Fc part of immunoglobulins exhibit high virus neutralization efficiency, but the structure and stability of these molecules are poorly understood. We show that although the hinge between the ACE2 and the IgG4-Fc is highly flexible, the conformational dynamics of the two ACE2 domains is restricted by their association.

Combining NMR, SAXS and SANS to characterize the structure and dynamics of protein complexes.

Understanding the structure and dynamics of biological macromolecules is essential to decipher the molecular mechanisms that underlie cellular functions. The description of structure and conformational dynamics often requires the integration of complementary techniques. In this review, we highlight the utility of combining nuclear magnetic resonance (NMR) spectroscopy with small angle scattering (SAS) to characterize these challenging biomolecular systems.

NudC guides client transfer between the Hsp40/70 and Hsp90 chaperone systems.

In the eukaryotic cytosol, the Hsp70 and the Hsp90 chaperone machines work in tandem with the maturation of a diverse array of client proteins. The transfer of nonnative clients between these systems is essential to the chaperoning process, but how it is regulated is still not clear. We discovered that NudC is an essential transfer factor with an unprecedented mode of action: NudC interacts with Hsp40 in Hsp40-Hsp70-client complexes and displaces Hsp70.

Client binding shifts the populations of dynamic Hsp90 conformations through an allosteric network.

Hsp90 is a molecular chaperone that interacts with a specific set of client proteins and assists their folding. The underlying molecular mechanisms, involving dynamic transitions between open and closed conformations, are still enigmatic. Combining nuclear magnetic resonance, small-angle x-ray scattering, and biochemical experiments, we have identified a key intermediate state of Hsp90 induced by adenosine triphosphate (ATP) binding, in which rotation of the Hsp90 N-terminal domain (NTD) yields a domain arrangement poised for closing.

FARS1-related disorders caused by bi-allelic mutations in cytosolic phenylalanyl-tRNA synthetase genes: Look beyond the lungs!

Aminoacyl-tRNA synthetases (ARSs) catalyze the first step of protein biosynthesis (canonical function) and have additional (non-canonical) functions outside of translation. Bi-allelic pathogenic variants in genes encoding ARSs are associated with various recessive mitochondrial and multisystem disorders. We describe here a multisystem clinical phenotype based on bi-allelic mutations in the two genes (FARSA, FARSB) encoding distinct subunits for tetrameric cytosolic phenylalanyl-tRNA synthetase (FARS1).

Interaction of protocadherin-15 with the scaffold protein whirlin supports its anchoring of hair-bundle lateral links in cochlear hair cells.

The hair bundle of cochlear hair cells is the site of auditory mechanoelectrical transduction. It is formed by three rows of stiff microvilli-like protrusions of graduated heights, the short, middle-sized, and tall stereocilia. In developing and mature sensory hair cells, stereocilia are connected to each other by various types of fibrous links.

Deciphering the Unexpected Binding Capacity of the Third PDZ Domain of Whirlin to Various Cochlear Hair Cell Partners.

Hearing is a mechanical and neurochemical process, which occurs in the hair cells of inner ear that converts the sound vibrations into electrical signals transmitted to the brain. The multi-PDZ scaffolding protein whirlin plays a critical role in the formation and function of stereocilia exposed at the surface of hair cells. In this article, we reported seven stereociliary proteins that encode PDZ binding motifs (PBM) and interact with whirlin PDZ3, where four of them are first reported.

When Less Is More: Combining Site-Specific Isotope Labeling and NMR Unravels Structural Details of Huntingtin Repeats.

In this issue of Structure, Urbanek et al. (2020a) combine site-specific isotope labeling and NMR spectroscopy to investigate opposing effects of flanking regions onto the conformation of the poly-Q region in Huntingtin. Poly-Q interactions with preceding residues promote an α-helical conformation while a following proline-rich region favors extended conformations.

Current approaches for integrating solution NMR spectroscopy and small-angle scattering to study the structure and dynamics of biomolecular complexes.

The study of complex and dynamic biomolecular assemblies is a key challenge in structural biology and requires the use of multiple methodologies providing complementary spatial and temporal information. NMR spectroscopy is a powerful technique that allows high-resolution structure determination of biomolecules as well as investigating their dynamic properties in solution. However, for high-molecular-weight systems, such as biomolecular complexes or multi-domain proteins, it is often only possible to obtain sparse NMR data, posing significant challenges to structure determination.

Evolutionary divergent PEX3 is essential for glycosome biogenesis and survival of trypanosomatid parasites.

Trypanosomatid parasites cause devastating African sleeping sickness, Chagas disease, and Leishmaniasis that affect about 18 million people worldwide. Recently, we showed that the biogenesis of glycosomes could be the "Achilles' heel" of trypanosomatids suitable for the development of new therapies against trypanosomiases. This was shown for inhibitors of the import machinery of matrix proteins, while the distinct machinery for the topogenesis of glycosomal membrane proteins evaded investigation due to the lack of a druggable interface.

Structure-based optimization of a PDZ-binding motif within a viral peptide stimulates neurite outgrowth.

Protection of neuronal homeostasis is a major goal in the management of neurodegenerative diseases. Microtubule-associated Ser/Thr kinase 2 (MAST2) inhibits neurite outgrowth, and its inhibition therefore represents a potential therapeutic strategy. We previously reported that a viral protein (G-protein from rabies virus) capable of interfering with protein-protein interactions between the PDZ domain of MAST2 and the C-terminal moieties of its cellular partners counteracts MAST2-mediated suppression of neurite outgrowth.

Potentiation of ABCA3 lipid transport function by ivacaftor and genistein.

ABCA3 is a phospholipid transporter implicated in pulmonary surfactant homoeostasis and localized at the limiting membrane of lamellar bodies, the storage compartment for surfactant in alveolar type II cells. Mutations in ABCA3 display a common genetic cause for diseases caused by surfactant deficiency like respiratory distress in neonates and interstitial lung disease in children and adults, for which currently no causal therapy exists. In this study, we investigated the effects of ivacaftor and genistein, two potentiators of the cystic fibrosis transmembrane conductance regulator (CFTR), on ABCA3-specific lipid transport function.

Structural plasticity of the HHD2 domain of whirlin.

Whirlin is a protein essential to sensory neurons. Its defects are responsible for nonsyndromic deafness or for the Usher syndrome, a condition associating congenital deafness and progressive blindness. This large multidomain scaffolding protein is expressed in three isoforms with different functions and localizations in stereocilia bundles of hearing hair cells or in the connecting cilia of photoreceptor cells.

Structural Characterization of Whirlin Reveals an Unexpected and Dynamic Supramodule Conformation of Its PDZ Tandem.

Hearing relies on the transduction of sound-evoked vibrations into electric signals, occurring in the stereocilia bundle of hair cells. The bundle is organized in a staircase pattern formed by rows of packed stereocilia. This architecture is pivotal to transduction and involves a network of scaffolding proteins with hitherto uncharacterized features.

(1)H, (13)C and (15)N backbone resonance assignments and dynamic properties of the PDZ tandem of Whirlin.

Mammals perceive sounds thanks to mechanosensory hair cells located in the inner ear. The stereocilia of these cells are tightly bound together in bundles by a network of cadherins and scaffolding proteins. Stereocilia deflection induces stretching of this network and is responsible for hair cell depolarization that triggers the neuronal message, transducing the mechanical signal into an electric signal transmissible to the brain.

Deciphering the unconventional peptide binding to the PDZ domain of MAST2.

Phosphatase and tensin homologue (PTEN) and microtubule-associated serine threonine kinase 2 (MAST2) are key negative regulators of survival pathways in neuronal cells. The two proteins interact via the PDZ (PSD-95, Dlg1, Zo-1) domain of MAST2 (MAST2-PDZ). During infection by rabies virus, the viral glycoprotein competes with PTEN for interaction with MAST2-PDZ and promotes neuronal survival.

Strategies to interfere with PDZ-mediated interactions in neurons: What we can learn from the rabies virus.

PDZ (PSD-95/Dlg/ZO-1) domains play a major role in neuronal homeostasis in which they act as scaffold domains regulating cellular trafficking, self-association and catalytic activity of essential proteins such as kinases and phosphatases. Because of their central role in cell signaling, cellular PDZ-containing proteins are preferential targets of viruses to hijack cellular function to their advantage. Here, we describe how the viral G protein of the rabies virus specifically targets the PDZ domain of neuronal enzymes during viral infection.

Selectivity, cocrystal structures, and neuroprotective properties of leucettines, a family of protein kinase inhibitors derived from the marine sponge alkaloid leucettamine B.

DYRKs (dual specificity, tyrosine phosphorylation regulated kinases) and CLKs (cdc2-like kinases) are implicated in the onset and development of Alzheimer's disease and Down syndrome. The marine sponge alkaloid leucettamine B was recently identified as an inhibitor of DYRKs/CLKs. Synthesis of analogues (leucettines) led to an optimized product, leucettine L41.