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The ability to detect low numbers of microbial cells in food and clinical samples is highly valuable but remains a challenge. Here we present a detection system (called ‘APC-Cas’) that can detect very low numbers of a bacterial pathogen without isolation, using a three-stage amplification to generate powerful fluorescence signals. APC-Cas involves a combination of nucleic acid-based allosteric probes and CRISPR-Cas13a components. It can selectively and sensitively quantify Salmonella Enteritidis cells (from 1 to 10 5 CFU) in various types of samples such as milk, showing similar or higher sensitivity and accuracy compared with conventional real-time PCR. Furthermore, APC-Cas can identify low numbers of S . Enteritidis cells in mouse serum, distinguishing mice with early- and late-stage infection from uninfected mice. Our method may have potential clinical applications for early diagnosis of pathogens. The detection of pathogens in food and clinical samples remains a challenge. Here, Shen et al. present a detection system, involving a combination of nucleic acid-based allosteric probes and CRISPR-Cas13a components, that can detect very low numbers of a bacterial pathogen in milk and serum samples without isolation.

Mechanosensitive (MS) ion channels are a ubiquitous type of molecular force sensor sensing forces from the surrounding bilayer. The profound structural diversity in these channels suggests that the molecular mechanisms of force sensing follow unique structural blueprints. Here we determine the structures of plant and mammalian OSCA/TMEM63 proteins, allowing us to identify essential elements for mechanotransduction and propose roles for putative bound lipids in OSCA/TMEM63 mechanosensation. Briefly, the central cavity created by the dimer interface couples each subunit and modulates dimeric OSCA/TMEM63 channel mechanosensitivity through the modulating lipids while the cytosolic side of the pore is gated by a plug lipid that prevents the ion permeation. Our results suggest that the gating mechanism of OSCA/TMEM63 channels may combine structural aspects of the ‘lipid-gated’ mechanism of MscS and TRAAK channels and the calcium-induced gating mechanism of the TMEM16 family, which may provide insights into the structural rearrangements of TMEM16/TMC superfamilies. Mechanosensitive channels exhibit large structural variations. Here, the authors reveal that OSCA channels exhibit different oligomeric states and are gated/regulated by lipids at different locations in response to physical forces.

MicroRNAs (miRNAs) have been widely investigated as potential biomarkers for early clinical diagnosis of cancer. Developing an miRNA detection platform with high specificity, sensitivity, and exploitability is always necessary. Electrochemiluminescence (ECL) is an electrogenerated chemiluminescence technology that greatly decreases background noise and improves detection sensitivity. The development of a paper‐based ECL biosensor further makes ECL suitable for point‐of‐care detection. Recently, clustered regularly interspaced short palindromic repeats (CRISPR)/Cas13a as high‐fidelity, efficient, and programmable CRISPR RNA (crRNA) guided RNase has brought a next‐generation biosensing technology. However, existing CRISPR/Cas13a based detection often faces a trade‐off between sensitivity and specificity. In this research, a CRISPR/Cas13a powered portable ECL chip (PECL‐CRISPR) is constructed. Wherein target miRNA activates Cas13a to cleave a well‐designed preprimer, and triggers the subsequent exponential amplification and ECL detection. Under optimized conditions, a limit‐of‐detection of 1 × 10−15 m for miR‐17 is achieved. Through rationally designing the crRNA, the platform can provide single nucleotide resolution to dramatically distinguish miRNA target from its highly homologous family members. Moreover, the introduction of “light‐switch” molecule [Ru(phen)2dppz]2+ allows the platform to avoid tedious electrode modification and washing processes, thereby simplifying the experimental procedure and lower testing cost. Analysis results of miRNA from tumor cells also demonstrate the PECL‐CRISPR platform holds a promising potential for molecular diagnosis. A clustered regularly interspaced short palindromic repeats (CRISPR)/Cas13a powered portable pBPE‐ECL chip (PECL‐CRISPR) is developed, which combines the high‐fidelity and trans‐cleavage of Cas13a, high efficiency of exponential amplification, high sensitivity and low background noise of electrochemiluminescence technology, and the simplicity of “light‐switch” [Ru(phen)2dppz]2+, thereby enabling ultrasensitive, highly‐specific, convenient, and low‐cost detection of miRNA.

The transmembrane voltage gradient is a general physico-chemical cue that regulates diverse biological function through voltage-gated ion channels. How voltage sensing mediates ion flows remains unknown at the molecular level. Here, we report six conformations of the human Eag2 (hEag2) ranging from closed, pre-open, open, and pore dilation but non-conducting states captured by cryo-electron microscopy (cryo-EM). These multiple states illuminate dynamics of the selectivity filter and ion permeation pathway with delayed rectifier properties and Cole-Moore effect at the atomic level. Mechanistically, a short S4-S5 linker is coupled with the constrict sites to mediate voltage transducing in a non-domain-swapped configuration, resulting transitions for constrict sites of F464 and Q472 from gating to open state stabilizing for voltage energy transduction. Meanwhile, an additional potassium ion occupied at positions S6 confers the delayed rectifier property and Cole-Moore effects. These results provide insight into voltage transducing and potassium current across membrane, and shed light on the long-sought Cole-Moore effects. Human Eag2 is a voltage-gated potassium channel with unique delayed rectifying gating kinetics. Here, authors show how voltage opens the channel and illuminate a mechanism of delayed rectifier gating.

OSCA/TMEM63 channels, which have transporter-like architectures, are bona fide mechanosensitive (MS) ion channels that sense high-threshold mechanical forces in eukaryotic cells. The activation mechanism of these transporter-like channels is not fully understood. Here we report cryo-EM structures of a dimeric OSCA/TMEM63 pore mutant OSCA1.1-F516A with a sequentially extracellular dilated pore in a detergent environment. These structures suggest that the extracellular pore sequential dilation resembles a flower blooming and couples to a sequential contraction of each monomer subunit towards the dimer interface and subsequent extrusion of the dimer interface lipids. Interestingly, while OSCA1.1-F516A remains non-conducting in the native lipid environment, it can be directly activated by lyso-phosphatidylcholine (Lyso-PC) with reduced single-channel conductance. Structural analysis of OSCA1.1-F516A in lyso-PC-free and lyso-PC-containing lipid nanodiscs indicates that lyso-PC induces intracellular pore dilation by attracting the M6b to upward movement away from the intracellular side thus extending the intracellular pore. Further functional studies indicate that full activation of MS OSCA/TMEM63 dimeric channels by high-threshold mechanical force also involves the opening of both intercellular and extracellular pores. Our results provide the fundamental activation paradigm of the unique transporter-like MS OSCA/TMEM63 channels, which is likely applicable to functional branches of the TMEM63/TMEM16/TMC superfamilies. How mechanosensitive OSCA/TMEM63 channels are activated remains a mystery. Here, the authors reveal the landscapes of the activation process of OSCA/TMEM63 channels.

PIEZO channels transmit mechanical force signals to cells, allowing them to make critical decisions during development and in pathophysiological conditions. Their fast/slow inactivation modes have been implicated in mechanopathologies but remain poorly understood. Here, we report several near-atomic resolution cryo-EM structures of fast-inactivating wild-type human PIEZO1 (hPIEZO1) and its slow-inactivating channelopathy mutants with or without its auxiliary subunit MDFIC. Our results suggest that hPIEZO1 has a more flattened and extended architecture than curved mouse PIEZO1 (mPIEZO1). The multi-lipidated MDFIC subunits insert laterally into the hPIEZO1 pore module like mPIEZO1, resulting in a more curved and extended state. Interestingly, the high-resolution structures suggest that the pore lipids, which directly seal the central hydrophobic pore, may be involved in the rapid inactivation of hPIEZO1. While the severe hereditary erythrocytosis mutant R2456H significantly slows down the inactivation of hPIEZO1, the hPIEZO1-R2456H-MDFIC complex shows a more curved and contracted structure with an inner helix twist due to the broken link between the pore lipid and R2456H. These results suggest that the pore lipids may be involved in the mechanopathological rapid inactivation mechanism of PIEZO channels.

Channelrhodopsins are popular optogenetic tools in neuroscience, but remain poorly understood mechanistically. Here we report the cryo-EM structures of channelrhodopsin-2 (ChR2) from Chlamydomonas reinhardtii and H. catenoides kalium channelrhodopsin (KCR1). We show that ChR2 recruits an endogenous N-retinylidene-PE-like molecule to a previously unidentified lateral retinal binding pocket, exhibiting a reduced light response in HEK293 cells. In contrast, H. catenoides kalium channelrhodopsin (KCR1) binds an endogenous retinal in its canonical retinal binding pocket under identical condition. However, exogenous ATR reduces the photocurrent magnitude of wild type KCR1 and also inhibits its leaky mutant C110T. Our results uncover diverse retinal chromophores with distinct binding patterns for channelrhodopsins in mammalian cells, which may further inspire next generation optogenetics for complex tasks such as cell fate control. It is known that channelrhodopsins use all-trans retinal as chromophore for light activation. Here, the authors find that different channelrhodopsins utilize various forms of retinal in mammalian cells, which could inspire next-generation optogenetic tools.

The regulation of CRISPR‒Cas activity is critical for developing advanced biotechnologies. Optical control of CRISPR‒Cas system activity can be achieved by modulation of Cas proteins or guide RNA (gRNA), but these approaches either require complex protein engineering modifications or customization of the optically modulated gRNAs according to the target. Here, we present a method, termed photocleavable phosphorothioate DNA (PC&PS DNA)-mediated regulation of CRISPR‒Cas activity (DNACas), that is versatile and overcomes the limitations of conventional methods. In DNACas, CRISPR‒Cas activity is silenced by the affinity binding of PC&PS DNA and restored through light-triggered chemical bond breakage of PC&PS DNA. The universality of DNACas is demonstrated by adopting the PC&PS DNA to regulate various CRISPR‒Cas enzymes, achieving robust light-switching performance. DNACas is further adopted to develop a light-controlled one-pot LAMP-BrCas12b detection method and a spatiotemporal gene editing strategy. We anticipate that DNACas could be employed to drive various biotechnological advances. CRISPR systems are powerful tools for gene editing and diagnostics, but their regulation is challenging. Here, the authors present DNACas, a light-controlled method using photocleavable phosphorothioate DNA to modulate CRISPR activity, enabling precise gene editing and one-pot diagnostic detection.

Phospholipids in cell membrane provide both regulatory and structural function of a cell. How lipid remodeling regulates cell fate remains less explored. Here we report the cryo-electron microscopy structure of TMEM164 identified by genome-wide CRISPR screen as an anti-ferroptotic factor. The overall architecture reveals a dimer of two 7 transmembrane domain monomers and a metal ion catalytic center with phospholipid substrate in a distinct polyunsaturated fatty acyl (PUFA)-C123 intermediate state. Both loss and gain of its function result in the decline of PUFA-ePE and elevation of C16/18:1-ePE, consequently confer resistance to GPX4 inhibitor RSL3 induced ferroptosis. Mutagenesis studies further validate critical residues for the catalytic center (C123) and the chelates center (E106, Y177 and H181). Through virtual screen and rational design, we identify and test candidate inhibitors for TMEM164, including activity for Montelukast S-enantiomer with 4 order of magnitude higher affinity. Our works not only demonstrates TMEM164 as a membrane lipid remodeler that controls the ferroptotic fate, but also highlights the power of integrating multi-scale platforms to unravel distinct mechanisms and functions. Phospholipid remodeling governs cell fate, yet its ferroptosis-related mechanisms remain elusive. Here, we report the cryo-EM structure of phospholipid remodeler TMEM164, identify its lipid remodeling mechanism, and discover Montelukast S- enantiomer as a potent inhibitor.