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Many proteins exist naturally as symmetrical homooligomers or homopolymers 1 . The emergent structural and functional properties of such protein assemblies have inspired extensive efforts in biomolecular design 2 – 5 . As synthesized by ribosomes, proteins are inherently asymmetric. Thus, they must acquire multiple surface patches that selectively associate to generate the different symmetry elements needed to form higher-order architectures 1 , 6 —a daunting task for protein design. Here we address this problem using an inorganic chemical approach, whereby multiple modes of protein–protein interactions and symmetry are simultaneously achieved by selective, ‘one-pot’ coordination of soft and hard metal ions. We show that a monomeric protein (protomer) appropriately modified with biologically inspired hydroxamate groups and zinc-binding motifs assembles through concurrent Fe 3+ and Zn 2+ coordination into discrete dodecameric and hexameric cages. Our cages closely resemble natural polyhedral protein architectures 7 , 8 and are, to our knowledge, unique among designed systems 9 – 13 in that they possess tightly packed shells devoid of large apertures. At the same time, they can assemble and disassemble in response to diverse stimuli, owing to their heterobimetallic construction on minimal interprotein-bonding footprints. With stoichiometries ranging from [2 Fe:9 Zn:6 protomers] to [8 Fe:21 Zn:12 protomers], these protein cages represent some of the compositionally most complex protein assemblies—or inorganic coordination complexes—obtained by design. An inorganic chemical approach to biomolecular design is used to generate ‘cages’ that can simultaneously promote symmetry and multiple modes of protein interactions.

The formation of condensed matter typically involves a trade-off between structural order and flexibility. As the extent and directionality of interactions between atomic or molecular components increase, materials generally become more ordered but less compliant, and vice versa. Nevertheless, high levels of structural order and flexibility are not necessarily mutually exclusive; there are many biological (such as microtubules 1 , 2 , flagella 3 , viruses 4 , 5 ) and synthetic assemblies (for example, dynamic molecular crystals 6 – 9 and frameworks 10 – 13 ) that can undergo considerable structural transformations without losing their crystalline order and that have remarkable mechanical properties 8 , 14 , 15 that are useful in diverse applications, such as selective sorption 16 , separation 17 , sensing 18 and mechanoactuation 19 . However, the extent of structural changes and the elasticity of such flexible crystals are constrained by the necessity to maintain a continuous network of bonding interactions between the constituents of the lattice. Consequently, even the most dynamic porous materials tend to be brittle and isolated as microcrystalline powders 14 , whereas flexible organic or inorganic molecular crystals cannot expand without fracturing. Owing to their rigidity, crystalline materials rarely display self-healing behaviour 20 . Here we report that macromolecular ferritin crystals with integrated hydrogel polymers can isotropically expand to 180 per cent of their original dimensions and more than 500 per cent of their original volume while retaining periodic order and faceted Wulff morphologies. Even after the separation of neighbouring ferritin molecules by 50 ångströms upon lattice expansion, specific molecular contacts between them can be reformed upon lattice contraction, resulting in the recovery of atomic-level periodicity and the highest-resolution ferritin structure reported so far. Dynamic bonding interactions between the hydrogel network and the ferritin molecules endow the crystals with the ability to resist fragmentation and self-heal efficiently, whereas the chemical tailorability of the ferritin molecules enables the creation of chemically and mechanically differentiated domains within single crystals. The integration of macromolecular ferritin protein crystals with hydrogel polymers gives a composite material that expands isotropically and reversibly to twice its size while maintaining periodicity, resists fragmentation and self-heals efficiently.

We report a bidirectional diversification and optimization campaign of the newly identified mu- and kappa-opioid receptor antagonist GB18, a naturally occurring Galbulimima alkaloid. First, we find that replacement of the GB18 piperidine with pyridine alters the pharmacology from antagonism to partial agonism, with reduced potency but markedly higher receptor selectivity for kappa- over mu-. Second, we optimize this hit via development of a mutually chemoselective cross-coupling of an alkyl iodide/vinyl triflate pair that leads to a series of low- and sub-nanomolar KOR-selective full agonists, some of which demonstrate bias for G protein activation over β-arrestin2 recruitment. Third, we advance three leads to in vivo (mouse) analysis and demonstrate brain penetrance and behavioral effects. In an open-field activity assay, we demonstrate that by increasing G protein signaling preference, agonists display an increase in exploratory, anxiolytic-like behaviors with no signs of sedation. The brevity and success of this campaign, combined with in vitro and in vivo pharmacology, demonstrate GB18 and its analogs as tractable new opioid scaffolds that allow favorable properties to be dialed in and unwanted properties removed.

Electrophilic halogenation is a widely used tool employed by medicinal chemists to either pre-functionalize molecules for further diversity or incorporate a halogen atom into drugs or drug-like compounds to solve metabolic problems or modulate off-target effects. Current methods to increase the power of halogenation rely on either the invention of new reagents or activating commercially available reagents with various additives such as Lewis or Brønsted acids, Lewis bases and hydrogen-bonding activators. There is a high demand for new reagents that can halogenate otherwise unreactive compounds under mild conditions. Here we report the invention of a class of halogenating reagents based on anomeric amides, taking advantage of the energy stored in the pyramidalized nitrogen of N–X anomeric amides as a driving force. These robust halogenating methods are compatible with a variety of functional groups and heterocycles, as exemplified on over 50 compounds (including 13 gram-scale examples and 1 flow chemistry scale-up). Electrophilic halogenation approaches often suffer from low reactivity and chemoselectivity when it comes to complex compounds. Now a class of halogenating reagents based on anomeric amides that can halogenate complex bioactive molecules with diverse functional groups and heterocycles has been developed. The higher reactivity of these anomeric amide reagents is attributed to the energy stored in the pyramidalized nitrogen.

The self-assembly of proteins into sophisticated multicomponent assemblies is a hallmark of all living systems and has spawned extensive efforts in the construction of novel synthetic protein architectures with emergent functional properties. Protein assemblies in nature are formed via selective association of multiple protein surfaces through intricate noncovalent protein–protein interactions, a challenging task to accurately replicate in the de novo design of multiprotein systems. In this protocol, we describe the application of metal-coordinating hydroxamate (HA) motifs to direct the metal-mediated assembly of polyhedral protein architectures and 3D crystalline protein–metal–organic frameworks (protein-MOFs). This strategy has been implemented using an asymmetric cytochrome cb 562 monomer through selective, concurrent association of Fe 3+ and Zn 2+ ions to form polyhedral cages. Furthermore, the use of ditopic HA linkers as bridging ligands with metal-binding protein nodes has allowed the construction of crystalline 3D protein-MOF lattices. The protocol is divided into two major sections: (1) the development of a Cys-reactive HA molecule for protein derivatization and self-assembly of protein–HA conjugates into polyhedral cages and (2) the synthesis of ditopic HA bridging ligands for the construction of ferritin-based protein-MOFs using symmetric metal-binding protein nodes. Protein cages are analyzed using analytical ultracentrifugation, transmission electron microscopy and single-crystal X-ray diffraction techniques. HA-mediated protein-MOFs are formed in sitting-drop vapor diffusion crystallization trays and are probed via single-crystal X-ray diffraction and multi-crystal small-angle X-ray scattering measurements. Ligand synthesis, construction of HA-mediated assemblies, and post-assembly analysis as described in this protocol can be performed by a graduate-level researcher within 6 weeks. To design new multiprotein systems, the authors describe how to combine natural metal-coordinating motifs and hydroxamic acid groups to direct metal-mediated assembly of polyhedral protein architectures and 3D crystalline protein frameworks.

Change history: In this Letter, Alexander Groisman should have been listed as an author. This error has been corrected online.Change history: In this Letter, Alexander Groisman should have been listed as an author. This error has been corrected online.

The self-assembly of proteins into sophisticated multicomponent assemblies is a hallmark of all living systems and has spawned extensive efforts in the construction of novel synthetic protein architectures with emergent functional properties. Protein assemblies in nature are formed via selective association of multiple protein surfaces through intricate noncovalent protein-protein interactions, a challenging task to accurately replicate in the de novo design of multiprotein systems. In this protocol, we describe the application of metal-coordinating hydroxamate (HA) motifs to direct the metal-mediated assembly of polyhedral protein architectures and 3D crystalline protein-metal-organic frameworks (protein-MOFs). This strategy has been implemented using an asymmetric cytochrome cb.sub.562 monomer through selective, concurrent association of Fe.sup.3+ and Zn.sup.2+ ions to form polyhedral cages. Furthermore, the use of ditopic HA linkers as bridging ligands with metal-binding protein nodes has allowed the construction of crystalline 3D protein-MOF lattices. The protocol is divided into two major sections: (1) the development of a Cys-reactive HA molecule for protein derivatization and self-assembly of protein-HA conjugates into polyhedral cages and (2) the synthesis of ditopic HA bridging ligands for the construction of ferritin-based protein-MOFs using symmetric metal-binding protein nodes. Protein cages are analyzed using analytical ultracentrifugation, transmission electron microscopy and single-crystal X-ray diffraction techniques. HA-mediated protein-MOFs are formed in sitting-drop vapor diffusion crystallization trays and are probed via single-crystal X-ray diffraction and multi-crystal small-angle X-ray scattering measurements. Ligand synthesis, construction of HA-mediated assemblies, and post-assembly analysis as described in this protocol can be performed by a graduate-level researcher within 6 weeks.