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There are as yet no licensed therapeutics for the COVID-19 pandemic. The causal coronavirus (SARS-CoV-2) binds host cells via a trimeric spike whose receptor binding domain (RBD) recognizes angiotensin-converting enzyme 2, initiating conformational changes that drive membrane fusion. We find that the monoclonal antibody CR3022 binds the RBD tightly, neutralizing SARS-CoV-2, and report the crystal structure at 2.4 Å of the Fab/RBD complex. Some crystals are suitable for screening for entry-blocking inhibitors. The highly conserved, structure-stabilizing CR3022 epitope is inaccessible in the prefusion spike, suggesting that CR3022 binding facilitates conversion to the fusion-incompetent post-fusion state. Cryogenic electron microscopy (cryo-EM) analysis confirms that incubation of spike with CR3022 Fab leads to destruction of the prefusion trimer. Presentation of this cryptic epitope in an RBD-based vaccine might advantageously focus immune responses. Binders at this epitope could be useful therapeutically, possibly in synergy with an antibody that blocks receptor attachment. • CR3022 binds the RBD of SARS-CoV-2 and shows strong neutralization • Neutralization is by destroying the prefusion spike conformation • CR3022 binds a highly conserved epitope that is inaccessible in prefusion spike protein • CR3022 could have therapeutic potential alone or in synergy with a receptor blocker Huo et al. find that the antibody CR3022 binds tightly to the receptor binding domain of the SARS-CoV-2 spike at a site different to that used by the receptor. CR3022 effectively neutralizes the virus, and cryo-EM reveals that it disrupts the spike. Such antibodies could have potential as COVID-19 therapeutics. [ABSTRACT FROM AUTHOR]

The Sonic Hedgehog (SHH) morphogen pathway is fundamental for embryonic development and stem cell maintenance and is implicated in various cancers. A key step in signaling is transfer of a palmitate group to the SHH N terminus, catalyzed by the multi-pass transmembrane enzyme Hedgehog acyltransferase (HHAT). We present the high-resolution cryo-EM structure of HHAT bound to substrate analog palmityl-coenzyme A and a SHH-mimetic megabody, revealing a heme group bound to HHAT that is essential for HHAT function. A structure of HHAT bound to potent small-molecule inhibitor IMP-1575 revealed conformational changes in the active site that occlude substrate binding. Our multidisciplinary analysis provides a detailed view of the mechanism by which HHAT adapts the membrane environment to transfer an acyl chain across the endoplasmic reticulum membrane. This structure of a membrane-bound O -acyltransferase (MBOAT) superfamily member provides a blueprint for other protein-substrate MBOATs and a template for future drug discovery. [Display omitted] • High-resolution cryo-EM structure of HHAT in complex with a SHH-mimetic megabody • Heme is bound to HHAT Cys324 in a membrane cavity and is essential for function • Palm-CoA binds in a central HHAT cavity adjacent to the catalytic histidine • The competitive inhibitor IMP-1575 causes conformational changes in the active site HHAT is a key enzyme in the Hedgehog signaling pathway and protein-substrate member of the membrane-bound O -acyltransferase (MBOAT) superfamily. Coupland et al. report the cryo-EM structures of HHAT bound to acyl-donor substrate, megabody, and inhibitor IMP-1575, providing insight into the structure-function relationship of HHAT, mechanism, and the basis for inhibition. [ABSTRACT FROM AUTHOR]