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16 pags, 7 figs . -- The online version contains supplementary movie1: https://static-content.springer.com/esm/art%3A10.1038%2Fs41467-021-27657-y/MediaObjects/41467_2021_27657_MOESM3_ESM.mp4, Tyrosine hydroxylase (TH) catalyzes the rate-limiting step in the biosynthesis of dopamine (DA) and other catecholamines, and its dysfunction leads to DA deficiency and parkinsonisms. Inhibition by catecholamines and reactivation by S40 phosphorylation are key regulatory mechanisms of TH activity and conformational stability. We used Cryo-EM to determine the structures of full-length human TH without and with DA, and the structure of S40 phosphorylated TH, complemented with biophysical and biochemical characterizations and molecular dynamics simulations. TH presents a tetrameric structure with dimerized regulatory domains that are separated 15 Å from the catalytic domains. Upon DA binding, a 20-residue α-helix in the flexible N-terminal tail of the regulatory domain is fixed in the active site, blocking it, while S40-phosphorylation forces its egress. The structures reveal the molecular basis of the inhibitory and stabilizing effects of DA and its counteraction by S40-phosphorylation, key regulatory mechanisms for homeostasis of DA and TH., This research was supported by the grant PID2019-105872GB-I00/AEI/10.13039/ 501100011033 from the Spanish Ministry of Science and Innovation to J.M.V. and J.C. as well as FRIMEDBIO (261826) from the Research Council of Norway to A.M.; the Western Norway Regional Health Authorities (912246 to A.M. and 912264 to R.K.), the K.G.

28 p.-5 fig.- + 4 fig. supl.-1 tab. supl., In most bacteriophages, genome transport across bacterial envelopes is carried out by the tail machinery. In viruses of the Podoviridae family, in which the tail is not long enough to traverse the bacterial wall, it has been postulated that viral core proteins assembled inside the viral head are translocated and reassembled into a tube within the periplasm that extends the tail channel. Bacteriophage T7 infects Escherichia coli, and despite extensive studies, the precise mechanism by which its genome is translocated remains unknown. Using cryo-electron microscopy, we have resolved the structure of two different assemblies of the T7 DNA translocation complex composed of the core proteins gp15 and gp16. Gp15 alone forms a partially folded hexamer, which is further assembled upon interaction with gp16 into a tubular structure, forming a channel that could allow DNA passage. The structure of the gp15–gp16 complex also shows the location within gp16 of a canonical transglycosylase motif involved in the degradation of the bacterial peptidoglycan layer. This complex docks well in the tail extension structure found in the periplasm of T7-infected bacteria and matches the sixfold symmetry of the phage tail. In such cases, gp15 and gp16 that are initially present in the T7 capsid eightfold-symmetric core would change their oligomeric state upon reassembly in the periplasm. Altogether, these results allow us to propose a model for the assembly of the core translocation complex in the periplasm, which furthers understanding of the molecular mechanism involved in the release of T7 viral DNA into the bacterial cytoplasm., This work was supported by the Ministry of Science,Innovation and Universities of Spain, Grant BFU 2014-54181 (to J.L.C.) and Contracts SEV-2013-0347 (to A.C.) and BES-2015-073615 to (M.P.-R.).

Nucleoplasmin (Np) is a pentameric histone chaperone that regulates the condensation state of chromatin in different cellular processes. We focus here on the interaction of NP with the histone octamer, showing that NP could bind sequentially the histone components to assemble an octamer-like particle, and crosslinked octamers with high affinity. The three-dimensional reconstruction of the Np/octamer complex generated by single-particle cryoelectron microscopy, revealed that several intrinsically disordered tail domains of two NP pentamers, facing each other through their distal face, encage the histone octamer in a nucleosome-like conformation and prevent its dissociation. Formation of this complex depended on post-translational modification and exposure of the acidic tract at the tail domain of NP. Finally, NP was capable of transferring the histone octamers to DNA in vitro, assembling nucleosomes. This activity may have biological relevance for processes in which the histone octamer must be rapidly removed from or deposited onto the DNA., This work was supported by Agencia Española de Investigación/Fondos de Desarrollo Regional (AEI/FEDER, UE), [BFU2016-75984 to J.M.V., BFU2016-75983 to A.M.] and the Basque Government [IT709-13 to A.M.]

The macromolecular machines of life use allosteric control to self-assemble, dissociate and change shape in response to signals. Despite enormous interest, the design of nanoscale allosteric assemblies has proven tremendously challenging. Here we present a proof of concept of allosteric assembly in which an engineered fold switch on the protein monomer triggers or blocks assembly. Our design is based on the hyper-stable, naturally monomeric protein CI2, a paradigm of simple two-state folding, and the toroidal arrangement with 6-fold symmetry that it only adopts in crystalline form. We engineer CI2 to enable a switch between the native and an alternate, latent fold that self-assembles onto hexagonal toroidal particles by exposing a favorable inter-monomer interface. The assembly is controlled on demand via the competing effects of temperature and a designed short peptide. These findings unveil a remarkable potential for structural metamorphosis in proteins and demonstrate key principles for engineering protein-based nanomachinery., European Research Council (grant ERC-2012-ADG-323059 to V.M.) and by the PRODESTECH network funded through the CONSOLIDER program from the Spanish Government (grant CSD2009-00088). L.A.C. acknowledges support from Ministry of Economy and Competitiveness through grants BIO2016-78768-P and RYC-2013-13197.