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Biology subjects

Park, D.

Publications and source records attributed to Park, D..

At least 19 recordsLinked to original sources

Efficient biological design via genomic in-context learning

In-context learning (ICL), the ability to perform new tasks from a few examples supplied in a prompt, is a defining emergent capability of large language models. Here, we show that ICL emerges in the genome language model Evo 2 and enables biological design. With as few as four examples in the prompt and no additional training, Evo 2 generates realistic metal-binding proteins, de novo antibodies, protein-RNA systems, and entire bacteriophage genomes. For {Phi}X174-like bacteriophage design, ICL surpasses previously fine-tuned models on computational measures of design quality and diversity. Beyond {Phi}X174, conditioning the model with different phage prompts enables us to efficiently design MS2 and M13 genomes in silico without fine-tuning. Iteratively updating the prompt with newly generated phage genomes, which we refer to as genomic chain-of-thought, further improves the diversity of designs while maintaining quality metrics. Paired with an inference engine that accelerates generation up to 35-fold and extends practicable context to a megabase, these results establish ICL as a versatile and efficient paradigm for biological sequence design.

bioinformatics↗

Allele-specific expression is associated with lower translational efficiency in mouse embryos and stem cells

An mRNA's cytoplasmic fate can be shaped by its transcriptional history, its modifications and associated protein complexes. Allele-specific expression (ASE), in which a gene's two alleles are transcribed unequally, provides a natural experiment given that the alleles can differ in sequence or chromatin state, yet their transcripts share the same cytoplasm. We previously found lower translational efficiency (TE) among genes with ASE in early mouse embryos. Because that observation came from one cross direction and from preimplantation stages only, sequence-dependent and parent-of-origin-dependent ASE could not be separated, and whether the association held in other cell types remained unknown. Here we addressed both by generating RNA sequencing and ribosome profiling data from reciprocal-cross mouse 8-cell embryos, individual embryonic stem cell clones, neural progenitor cells, and adult tissues. In 8-cell embryos, both sequence-dependent and parent-of-origin-dependent ASE were associated with lower TE. Genes with ASE at the 8-cell stage also had lower protein abundance at the subsequent morula stage. Ribo-ITP, which enables ribosome profiling from single clones, allowed assessing the relationship between ASE and TE in individual embryonic stem cell clones. We found that TE was lower wherever a gene was allelically imbalanced, and the reduction was larger where that imbalance was consistent across clones. The same association held in neural progenitors, and when ASE was defined from independent published datasets, but was not detected in adult tissues. Allelic imbalance in transcription is therefore accompanied by reduced translation of the resulting mRNAs, though the intermediate carrying allelic information to the translation machinery remains unidentified.

molecular biology↗

Laminin-511 protects pancreatic β-cells from cytokine-induced death through integrin-mediated pro-survival signaling and modulation of protein kinase C δ

During the progression of type 1 diabetes (T1D), the extracellular matrix (ECM) surrounding pancreatic islets is degraded concurrent with infiltration of autoreactive immune cells and {beta}-cell death. Among the lost ECM proteins, laminin-511 is known to be essential for islet survival under healthy and T1D associated conditions, including high levels of pro-inflammatory cytokines. However, the key {beta}-cell signaling pathways regulated by laminin and the contributions to T1D pathogenesis when these cues are lost are poorly understood. This study utilizes a biomimetic reverse thermal gel (RTG) with laminin-511 to determine if laminin protects {beta}-cells against cytokine-induced death and elucidate the signaling pathways involved. MIN6 cells, C57Bl/6 mouse islets and human islets were encapsulated in RTG scaffolds with laminin-511 and treated with a cytokine cocktail for 24 hours. Islet viability and the activities of several pro- and anti-apoptotic proteins were studied. Laminin-511 was shown to protect islets against cytokine-induced death by interacting with {beta}1 integrins and activating pro-survival Akt signaling. Pro-survival signaling was mediated by reduced activity of protein kinase C{delta} (PKC{delta}), a key mediator of cytokine-induced {beta}-cell death, at the cell membrane in the presence of laminin via reduced levels of diacylglycerol (DAG), a canonical activator of PKC{delta}. Taken together, these results demonstrate that laminin-511 is an essential factor in protecting {beta}-cells against cytokine-induced death by downregulation of membrane DAG, inhibiting activation of pro-apoptotic PKC{delta}. Our results suggest that loss of ECM in T1D may make {beta}-cells more susceptible to cytokine-induced death by increasing activation of PKC{delta}. HighlightsO_LILaminin-511 improves islet survival under cytokine treatment C_LIO_LIPro-survival Akt is upregulated by laminin-511 C_LIO_LIPro-apoptotic PKC{delta} activity is downregulated at the cell membrane by laminin-511 C_LIO_LILaminin-511 decreases membrane DAG levels leading to reduced PKC{delta} activation C_LIO_LILaminin-511 is an essential ECM component for islet survival during type 1 diabetes C_LI

cell biology↗

Anticipatory modulation of motor unit discharge rate before rapid isometric elbow flexion force production

Surface electromyography (EMG) studies have demonstrated anticipatory muscle activation prior to predictable voluntary actions. However, the mechanism through which this preparation is expressed, whether through motor-unit recruitment or discharge-rate modulation, remains to be elucidated. We employed surface decomposition EMG to quantify motor-unit behavior prior to self-paced rapid isometric elbow-flexion force pulses. Twelve healthy young men were instructed to generate elbow-flexion pulse force at 30%, 40%, and 50% of the maximal voluntary contraction (MVC) at a self-selected time. Motor-unit activity was decomposed from the biceps brachii and triceps brachii muscles, and the normalized active motor-unit number and mean discharge rate were analyzed prior to pulse onset. In the agonist, the pre-pulse increase mean discharge rate exhibited a higher value than the change in detected motor-unit count, particularly at the 40% and 50% MVC targets. The discharge-rate increase scaled with the target force, with a heightened response observed in high-threshold as compared to low-threshold motor units. Antagonist recordings with sufficient decomposition yield exhibited a similar discharge-rate-dominant pattern; however, these data were available from a smaller sample size. Present findings suggest that discharge-rate modulation is a primary motor-unit-level feature of anticipatory preparation for rapid isometric force production.

neuroscience↗

ATAD3A structurally links mtDNA replication and mitochondrial fission

Mitochondrial function depends on the maintenance of its genome, and disruptions in copy number and distribution are hallmarks of mitochondrial disorders. Mitochondrial DNA (mtDNA) replication is spatially and temporally linked to mitochondrial division (i.e., fission). However, the signal that coordinates these two events, which are physically separated by the barrier of two mitochondrial membranes, remains unknown. To gain insight into this coordination, we employed correlative cryo-electron tomography (cryo-ET) to analyze the microenvironment surrounding replicating nucleoids. Mitochondrial regions containing replicating mtDNA exhibit a unique membrane architecture defined by the presence of clustered, membrane-spanning tethers that traverse the inner membrane space. Using a combination of superresolution microscopy and genetically encoded cryo-ET tagging technology, we identify these tethers as the AAA+ ATPase ATAD3A. We further show that ATAD3A knockdown reduces recruitment of the mitochondrial fission machinery, whereas overexpression promotes its recruitment and subsequent fission. Our work suggests that ATAD3A forms nanoscale linkages that coordinate these two distinct processes, revealing a new structural paradigm for organellar communication across distinct membrane-defined environments. HighlightsO_LIReplicating mitochondrial DNA (mtDNA) nucleoids are surrounded by a distinct membrane microenvironment. C_LIO_LIATAD3A forms membrane-spanning tethers enriched at replicating mtDNA sites. C_LIO_LIATAD3A enrichment is necessary and sufficient to recruit mitochondrial fission machinery and induce fission at mtDNA replication sites. C_LIO_LIATAD3A structurally couples mtDNA replication state to mitochondrial fission across distinct organellar subcompartments. C_LI

Cell Biology↗

Telomere-to-telomere, accurate, and gapless genome assembly (TTAGGA) of the Korean Jindo dog with a single-contig Y chromosome

Complete canine reference genomes are essential for studies of structural variation, sex-chromosome evolution, and breed-specific architecture, yet existing references remain incomplete on the Y chromosome and retain internal gaps across multiple chromosomes. Here, we introduce TTAGGA (Telomere-to-Telomere, Accurate, Gapless Genome Assembly), a stricter completeness standard requiring chromosomes assembled end-to-end with zero internal gaps and Merqury consensus QV [≥] 50, and present Jindo1-G-TTAGGA, the first canine assembly to meet this standard, achieved under a stringent QV [≥] 60 threshold. From 813 Gb ([~]340x coverage) of multi-platform data (PacBio HiFi [~]150x, ONT ultra-long [~]103x, parental Illumina [~]40x per parent) generated from a male Korean Jindo dog, trio binning with hifiasm produced two haplotype-resolved assemblies of 2,441.6 Mb (Hap1, maternal, chrX-carrying) and 2,340.5 Mb (Hap2, paternal, chrY-carrying). Both haplotypes are gap-free at every internal position, with canonical telomeric repeats verified at both ends of all 39 chromosomes (tidk), Merqury consensus QV of 78.0 (Hap1) and 76.8 (Hap2), trio switch-error rates below 0.13%, BUSCO completeness of 99.3% (Hap1) and 96.4% (Hap2; the lower value reflects absent X-linked orthologues in the Y-bearing haplotype), and Genome Continuity Index values of 98.2 (Hap1) and 94.7 (Hap2). Hap2 carries a single 21,255,890 bp gap-free Y chromosome with TTAGGG telomeric repeats at the q-arm terminus and an acrocentric satellite-rich p-arm, representing a 5.4-fold increase over the 3.94 Mb chrY of ROS_Cfam_1.0 and adding approximately 14 Mb of newly resolved Y-linked sequence; this corresponds to roughly 79% of the cytogenetically estimated 27 Mb full-length canine chrY. Jindo1-G-TTAGGA provides a chromosome-scale, haplotype-resolved, gap-free canine reference for studies of canine structural variation, sex-chromosome evolution, and canid phylogenomics.

genomics↗

Expansion Revealing of Pathology Resolves Nanostructures Associated with Inflammatory Phenotypes in COVID-19 Decedent Human Brain Tissue

Expansion revealing (ExR) elucidates cellular organization by separating proteins within dense nanostructures by 20x linear expansion, but requires fixation procedures incompatible with human pathology specimens. Here, we report ExR of pathology (ExRPath), which attains [~]20 nm resolution and decrowding of such tissues, through iterative 20x expansion, adapted to human brain pathology specimens. We also report a single-shot 15x expansion protocol for such tissues (15ExMPath), achieved through one-shot 15x expansion. Applying ExRPath and 15ExMPath to COVID-19-decedent brain tissue reveals periodic amyloid nanoclusters that co-localize with SARS-CoV-2 in a rare minority of patient specimens, pointing to a potential neuroinflammatory phenotype associated with COVID-19, and highlighting the power of high-throughput nanoimaging, empowered by expansion microscopy, for discovering potential novel disease mechanisms.

neuroscience↗

A mosaic of genomic architectures underpins parasitism loss in a jawless vertebrate

Lampreys are the only ancestrally parasitic vertebrate lineage, yet parasitism has been repeatedly lost alongside a suite of life-history changes, such as loss of migration and juvenile feeding and accelerated maturation. Combining whole-genome resequencing, haplotype-resolved assemblies, hybrid-zone genotyping, multi-tissue transcriptomics, and sperm phenotyping, we map this life-history syndrome in European Lampetra to six chromosomes spanning a mosaic of genomic architectures: a [~]20 Mb low-recombination region on chromosome 1 lacking chromosomal rearrangements within Lampetra but involving inter-specific rearrangements across deep lamprey lineages; a translocated inversion with ecotype-dependent sperm-velocity effects; and ecotype-divergent deletions overlapping genes crucial for nervous system (CNTNAP2) and reproductive development (FSHR). However, this genomic basis is not shared with a convergent sister lineage, pointing to independent routes to a recurring life-history transition in lampreys.

evolutionary biology↗

Evidence that injury can cause Drosophila gut differentiated, polyploid enterocytes to be recruited as stem cells via paligenosis

Differentiated cells can return to a progenitor-like state in response to injury via the evolutionarily conserved cellular program called paligenosis. Paligenosis proceeds by three stages: 1) autophagy/autodegradation of differentiated cell architecture, 2) metaplasia/progenitor gene induction, 3) TOR complex 1 (TORC1)-dependent cell cycle re-entry. Using multiple injury and reverse-lineage-tracing approaches in the Drosophila gut, we show that mature polyploid enterocytes dedifferentiate into diploid progenitors in response to epithelial injury. Several key findings suggest a role for paligenosis. Shortly after injury, enterocytes dramatically increased autophagic flux (stage 1); additionally, pharmacological and genetic inhibition of autophagy blocked progenitor recruitment. Rapamycin also blocked recruitment, indicating that TORC1 is required (stage 3). Finally, RNAi knockdown of ifrd1, an evolutionarily conserved protein required for paligenosis, blocked progenitor recruitment. Thus, replenishment of diploid progenitors from differentiated polyploid cells may occur by paligenosis. The Drosophila gut may offer a versatile system for dissecting the mechanisms of this evolutionarily conserved pathway. Impact StatementMature, polyploid Drosophila enterocytes may dedifferentiate to a stem cell-like, diploid state via the paligenosis cell regeneration program, adding to evidence that paligenosis is a fundamental cellular process and highlighting Drosophila gut as a potential model system for its study.

developmental biology↗

Transient activation of potent progenitor cells is required for spinal cord regeneration

Adult zebrafish exhibit full recovery following spinal cord injury. Transient expansion of stem cell-like progenitors is thought to underlie their regenerative capacity. Yet, our understanding of the identities and contributions of the crucial stem cell populations that direct spontaneous neural repair remains limited. Moreover, while most neural regeneration research is centered on promoting proliferative repair, the regulatory mechanisms that reinstate quiescence post-repair are unknown. Here, we determined the molecular identities and cellular contributions of sox2+ progenitors during spinal cord repair. Genetic lineage tracing shows zebrafish spinal progenitors, while quiescent in uninjured tissues, self-renew and differentiate into neurons and glia after injury. By single-cell sequencing, sox2+ cells are heterogeneous and biased towards neuronal or glial fates in both homeostatic and regenerating tissues. By screening for transcription factors that are differentially expressed in acute versus chronic spinal cord injury, we find the Bach1 transcription factors control transient progenitor cell activation by acting as dual activators and repressors of sox2 expression. This study elucidates the molecular diversity and contributions of sox2 expressing cells during spinal cord repair and identifies a transcriptional regulatory switch by which progenitor cells expand after injury and restore quiescence after regeneration is completed.

neuroscience↗

CAR-T-drug conjugate against solid tumor

Chimeric antigen receptor (CAR)-T cell therapy has been clinically successful in hematologic cancers but faces challenges in solid tumors, primarily due to limited tumor infiltration, immunosuppressive tumor microenvironments (TME), and antigen heterogeneity. While combining CAR-T cell therapy with chemotherapy can enhance antitumor activity, this often leads to substantial systemic toxicity. In this study, we introduce CAR-T-drug conjugate (CAR-T-D-C), a new class of dual-functional therapeutics that effectively addresses these obstacles by integrating click chemistry for precise conjugation of cytotoxic agents onto antigen-specific CAR-T cells. By transforming the hostile TME into an ally, this approach facilitates localized delivery of cytotoxic payload directly to the tumor site, enhancing the overall effectiveness of CAR-T therapy in solid tumors. CAR-T-D-Cs with different CAR-T cell binders exhibit robust antitumor activity across diverse solid tumor models, including both human tumor xenografts and syngeneic models. Spatial transcriptomic studies reveals that CAR-T-D-C achieves improved CAR-T tumor infiltration and functional activation within the TME. Compared to conventional CAR-T therapy, CAR-T-D-C markedly enhances immune cell infiltration, augments effector functions, promotes antigen spreading, amplifies systemic immune responses, and improves overall anti-tumor immunity. CAR-T-D-C represents a versatile therapeutic concept that combines the potency of small molecule drugs and the specificity of CAR-T cells as a 2-in-1 immunochemotherapy for treatment of solid tumors.

immunology↗

Imprinted antibody lineages can persist for half a century and dominate cross-neutralizing recall responses to poliovirus

Humoral immunity depends on a dynamic interplay between circulating polyclonal IgG antibodies and long-lived memory B cells (MBC). To elucidate this relationship, we integrated B-cell receptor sequencing with plasma IgG immunoproteomics to identify and quantify the recall response (plasma IgG and MBC) to inactivated poliovirus vaccine (IPV) in eight adults, 24-55 years after their childhood immunization. IPV immunization elicited highly skewed plasma IgG recall repertoires, dominated by a small subset ([~]8%) of total antibody lineages that were detectable prior to boosting (i.e., "pre-existing"). These IgG lineages spiked logarithmically in abundance ([~]102-104 fold-increase) and potently cross-neutralized multiple PV serotypes in vitro (titers [≥] 1:105). Notably, these dominant plasma IgG lineages were clonally linked to class-switched MBCs that circulated in blood 21 days post-boost and bore heavily mutated VH and VL variable region genes. Importantly, IPV-primed ex vivo B-cell cultures (MIMIC, Modular IMmune In vitro Construct) yielded clonal expansions that mirrored the dominant post-boost plasma IgG lineages in vivo, providing an in vitro mechanistic correlate of recall immunity. Together these findings demonstrate a decades-long interconnectivity between persistent MBC clones and the serological IgG repertoire. They further highlight the central role of immunological imprinting, whereby cross-reactive MBC clones--originally primed in childhood--can be reactivated to dominate the circulating IgG recall response more than 50 years after initial exposure.

immunology↗

Sensitizing tumor response to topoisomerase I antibody drug conjugate by selective CDK7 inhibition

This study investigates the transcriptional impact of Q901, a highly selective CDK7 inhibitor in clinical development. Q901 primarily disrupted MYC and E2F-dependent transcription program, downregulating cell cycle control and DNA damage repair pathways. CDK7 binding at the promoter-proximal regions was dramatically stabilized by Q901, leading to reduced occupancy of MYC, E2F, and RNA Polymerase II (RNAPII). These findings offered a novel therapeutic strategy to enhance cancer susceptibility to TOP1-DNA protein crosslinks (TOP1-DPCs) induced by TOP1 inhibitors. Resistance to TOP1 inhibitors arises through activation of DNA repair pathway when elongating RNAPII encounters TOP1-DPCs. By suppressing RNAPII transition from initiation to elongation and DNA repair pathways, Q901 stabilizes TOP1-DPCs and sensitizes tumor to TOP1 inhibitors. Preclinical studies demonstrated enhanced tumor suppression when combining Q901 with TOP1 inhibitor-based antibody-drug conjugates (TOP1i-ADCs), highlighting its potential as a therapeutic option for cancers resistant to TOP1i-ADC therapy. TeaserOvercoming ADC cross-resistance through combination approach.

cancer biology↗

A Precisely Controlled Long-Acting Immunosuppression Platform Enables Prolonged Survival of Vascularized Composite Allografts

Vascularized composite allotransplantation (VCA) restores complex tissue defects but demands lifelong systemic immunosuppression. Oral tacrolimus (TAC) is limited by a narrow therapeutic window, pharmacokinetic variability, adherence challenges, and toxicity. Local delivery could mitigate these issues, yet clinical translation has been hindered by burst release, short duration, and the inability to co-deliver agents. We developed PRECISE (Programmable, REtrievable, Controlled ImmunoSuppression Encapsulator), an injectable, in-situ-forming PLGA depot that achieves long-acting, tightly controlled TAC release via structure-guided co-formulation with drug-binding agents (DBAs). GRAS small molecules (e.g., EGCG, maltotriose) identified by in silico docking and in vitro screening suppressed burst and modulated solvent efflux. Notably, rapamycin (RAPA) served dually as an mTOR inhibitor and a TAC-binding excipient, enabling synchronized dual-agent delivery. PRECISE eliminated burst in vitro and produced coordinated TAC+RAPA release with clinically compatible injectability. In rats, monthly intragraft dosing maintained systemic TAC/RAPA within the therapeutic window ([~]5-10 ng/mL) for >300 days, prolonged hindlimb allograft survival, expanded Tregs, and induced donor-specific hyporesponsiveness. Surgical retrieval of the depot triggered rapid TAC decline, demonstrating reversibility. In a stringent, fully MHC-mismatched porcine VCA model, PRECISE maintained on-target drug levels and extended graft survival beyond 90 days with minimal rejection and preserved vascular integrity. PRECISE is, to our knowledge, the first retrievable, injectable platform to deliver long-acting, dual-agent immunosuppression with controlled kinetics, rapid attainment of therapeutic steady state, and sustained graft protection. Its modular, structure-guided design enables clinical translation across VCA and solid-organ transplantation, delivering precise, durable, and safer immunosuppression.

bioengineering↗

Inactivation of peptidoglycan remodeling promotes antibiotic susceptibility in vancomycin-resistant Enterococcus faecium

Vancomycin-resistant Enterococcus faecium (VREfm) is a leading cause of healthcare-associated infections globally and demands new approaches for treatment. Here we show that genetic and pharmacological inactivation of a highly conserved NlpC/P60 peptidoglycan hydrolase, secreted antigen A (SagA), enhanced vancomycin susceptibility of VREfm ex vivo and in vivo. Notably, genetic deletion of sagA impaired VREfm peptidoglycan remodeling, growth and increased the activity of vancomycin. We then identified first-in-class covalent NlpC/P60 peptidoglycan hydrolase inhibitors and demonstrated that pharmacological inactivation of SagA activity also impaired peptidoglycan remodeling and increased the efficacy of vancomycin across genetically distinct VREfm clinical isolates. Our study reveals peptidoglycan hydrolases are druggable targets whose inactivation improves the efficacy of vancomycin against VREfm.

microbiology↗

Screening channelrhodopsins using robotic intracellularelectrophysiology and single cell sequencing

BackgroundOur ability to engineer opsins is limited by an incomplete understanding of how sequence variations influence function. The vastness of opsin sequence space makes systematic exploration difficult. New methodIn recognition of the need for datasets linking opsin genetic sequence to function, we pursued a novel method for screening channel-rhodopsins to obtain these datasets. In this method, we integrate advances in robotic intracellular electrophysiology (Patch) to measure optogenetic properties (Excite), harvest individual cells of interest (Pick) and subsequently sequence them (Sequence), thus tying sequence to function. ResultsWe used this method to sequence more than 50 cells with associated functional characterization. We further demonstrate the utility of this method with experiments on heterogeneous populations of known opsins and single point mutations of a known opsin. Of these point mutations, we found C160W ablates ChrimsonRs response to light. Conclusion and comparison to existing methodsCompared to traditional manual patch clamp screening, which is labor-intensive and low-throughput, this approach enables more efficient, standardized, and scalable characterization of large opsin libraries. This method can enable opsin engineering with large datasets to increase our understanding of opsin sequence-function relationships.

neuroscience↗

Prenatal Environmental Determinants of Aromatase Brain-Promoter Methylation in Cord Blood: Chemical, Airborne, Pharmacological, and Nutritional Factors

Aromatase, an enzyme encoded by the gene CYP19A1, plays central roles in neurodevelopment. In the brain, its function is to convert androgens into neuroestrogens, ensuring balanced hormonal signalling. Both animal experiments and human studies have shown that, in males, disruption of aromatase, either genetically or epigenetically, can increase symptoms of autism. Prenatal exposure to bisphenol A (BPA), a common plastic chemical, can increase levels of DNA methylation--a key epigenetic modification--at the brain-specific CYP19A1 promoter, P1.f, reducing CYP19A1 expression. However, the extent to which other neurodevelopmentally relevant environmental exposures influence P1.f methylation remains unclear. Here, in the Barwon Infant Study (BIS) birth cohort (N = 906), we analysed the association between 25 prenatal exposures (from five classes previously linked to neurodevelopmental outcomes: manufactured chemicals, air pollution, and pharmacological, nutrition and sunlight-related factors) and methylation of the CYP19A1 P1.f promoter using Weighted Quantile Sum (WQS) regression. We found that the WQS mixture index, a weighted combination of the prenatal exposures, was positively associated with higher P1.f methylation (Adjusted Mean Difference (AMD) = 0.712 (95% CI 0.11, 1.315), p = 0.021), indicating reduced brain aromatase activity. Prenatal exposures with the strongest contribution to the mixture effect included bisphenols (including BPA), reduced sunlight, household mould, phthalates, low folate intake, and air pollution. These findings highlight epigenetic modification of the aromatase gene as a biologically plausible, convergent mechanism through which multiple environmental risk factors for autism may exert effects.

genomics↗

In-situ structures of the Legionella Dot/Icm T4SS identify the DotA-IcmX complex as the gatekeeper for effector translocation

The Dot/Icm machine in Legionella pneumophila is one of the most versatile type IV secretion systems (T4SSs), with a remarkable capacity to translocate over 330 different effector proteins across the bacterial envelope into host cells. At least 27 Dot and Icm proteins are required for assembly and function of the system, yet the architecture and activation mechanism remain poorly understood at the molecular level. Here, we deploy cryo-electron microscopy to reveal in-situ structures of the Dot/Icm machine at near-atomic resolution. Importantly, two proteins essential for effector translocation, DotA and IcmX, form a pentameric protochannel at an inactive state. Upon activation, the DotA-IcmX protochannel undergoes extensive rearrangements to form an extended transenvelope passage capable of transporting effector proteins from the bacterial cytoplasm into host cells as revealed by cryo-electron tomography. Collectively, our findings suggest that the DotA-IcmX complex functions as the gatekeeper for effector translocation of the Dot/Icm T4SS.

molecular biology↗