Biology subjects

Mozumdar, D.

Publications and source records attributed to Mozumdar, D..

7 recordsLinked to original sources

bioRxiv2026

A tripartite mechanism licenses RNA polymerase import into the phage nucleus

Nucleus-forming jumbo phages import a phage-encoded non-virion RNA polymerase (nvRNAP) into a proteinaceous nucleus, but how it is selected for import is unknown. Here, we identify an import pathway that couples nvRNAP subunit interactions with phage-encoded import factors. Maximal nvRNAP import requires a novel factor Imp7 (gp166) and the essential import factor Imp1. Imp7 is essential at environmental temperatures (20 C), where impaired nvRNAP import causes a profound loss of middle and late transcription and blocks phage DNA replication. Import of individual nvRNAP subunits also depends on other subunits, consistent with import licensing at the level of an assembled complex. In the absence of middle transcription and DNA replication, the phage nucleus surprisingly still assembles and segregates from the cytoplasm, demonstrating that nvRNAP nuclear localization and activity are not a critical checkpoint for nucleus assembly. Together, these findings define a specialized pathway for nuclear import of the multi-subunit RNAP and reveal that nuclear compartment assembly precedes the transcriptional and replicative programs required for its maturation.

microbiology↗

bioRxiv2025

Bacteriophage genome-wide transposon mutagenesis

Bacteriophages have genomes that span a wide size range, are densely packed with coding sequences, and frequently encode genes of unknown function. Classical forward genetics has defined essential genes for phage replication in a few model systems but remains laborious and non-scalable. Unbiased functional genomics approaches are therefore needed for phages, particularly for large lytic phages. Here, we develop a phage transposon sequencing (TnSeq) platform that uses the mariner transposase to insert an anti-CRISPR selectable marker into phage genomes. CRISPR-Cas13a-based enrichment of transposed phages followed by pooled sequencing identifies both fitness-conferring and dispensable genes. Using the Pseudomonas aeruginosa-infecting nucleus-forming jumbo phage {Phi}KZ (280,334 bp; 371 predicted genes) as a model, we show that [~]110 genes are fitness-conferring via phage TnSeq. These include conserved essential genes involved in phage nucleus formation, protein trafficking, transcription, DNA replication, and virion assembly. We also isolate hundreds of individual phages with insertions in non-essential genes and reveal conditionally essential genes that are specifically required in clinical isolates, at environmental temperature, or in the presence of a defensive nuclease. Phage TnSeq is a facile, scalable technology that can define essential phage genes and generate knockouts in all non-essential genes in a single experiment, enabling conditional genetic screens in phages and providing a broadly applicable resource for phage functional genomics.

microbiology↗

bioRxiv2024

Defining the constituents and functions of a lipid-based jumbo phage compartment

Viruses are vulnerable to cellular defenses at the start of the infection when a single copy genome has not yet initiated de novo viral protein synthesis. A family of jumbo phages related to phage {Phi}KZ, which infects Pseudomonas aeruginosa, uses a protein-based phage nucleus to protect the DNA during middle and late stages of infection, but how it is protected prior to phage nucleus assembly is unclear. To reveal the environment surrounding injected phage DNA, we determine which proteins interact with phage proteins injected with the phage genome. Here, we surprisingly identify host proteins related to membrane and lipid biology co-purifying with the injected phage protein. Staining of infected cells with lipophilic dyes revealed a clustering of host lipids co-localized with phage DNA and protein in an early phage infection (EPI) vesicle. Early gene expression is induced by the co-injected virion RNAP (vRNAP), with specific early proteins then associating with the EPI vesicle and ribosomes, likely to facilitate localized translation. As the infection progresses, the phage genome separates from the EPI vesicle and vRNAP, moving into the nascent proteinaceous phage nucleus. Enzymes involved in DNA replication and CRISPR/restriction immune nucleases notably do not localize to the EPI vesicle, supporting that DNA is not exposed at this early time point. We therefore propose that the EPI vesicle is rapidly constructed together with injected phage proteins, phage DNA, host lipids, and host membrane proteins to enable genome protection, early transcription, localized translation, and to ensure the faithful transfer of the single copy phage genome to the proteinaceous nucleus.

microbiology↗

bioRxiv2023

Next-generation interaction proteomics for quantitative Jumbophage-bacteria interaction mapping

Host-pathogen interactions (HPIs) are pivotal in regulating establishment, progression, and outcome of an infection. Affinity-purification mass spectrometry has become instrumental for the characterization of HPIs, however the targeted nature of exogenously expressing individual viral proteins has limited its utility to the analysis of relatively small pathogens. Here we present the use of co-fractionation mass spectrometry (SEC-MS) for the high-throughput analysis of HPIs from native viral infections of two jumbophages ({phi}KZ and{phi} PA3) in Pseudomonas aeruginosa. This enabled the detection >6000 unique host-pathogen and >200 pathogen-pathogen interactions for each phage, encompassing >50% of the phage proteome. Interactome-wide comparison across phages showed similar perturbed protein interactions suggesting fundamentally conserved mechanisms of phage predation within the KZ-like phage family. Prediction of novel ORFs revealed a{phi} PA3 complex showing strong structural and sequence similarity to{phi} KZ nvRNAp, suggesting{phi} PA3 also possesses two RNA polymerases acting at different stages of the infection cycle. We further expanded our understanding on the molecular organization of the virion packaged and injected proteome by identifying 23 novel virion components and 5 novel injected proteins, as well as providing the first evidence for interactions between KZ-like phage proteins and the host ribosome. To enable accessibility to this data, we developed PhageMAP, an online resource for network query, visualization, and interaction prediction (https://phagemap.ucsf.edu/). We anticipate this study will lay the foundation for the application of co-fractionation mass spectrometry for the scalable profiling of hostpathogen interactomes and protein complex dynamics upon infection.

systems biology↗

bioRxiv2022

Long-term, super-resolution HIDE imaging of the inner mitochondrial membrane in live cells with a cell-permeant lipid probe

The densely packed inner mitochondrial membrane (IMM) is vital for bioenergy generation and its dynamics control mitochondrial health and cellular homeostasis. IMM structure is complex, however, and imaging its dynamics with high temporal and spatial resolution is complicated by the photosensitivity of IMM-resident enzymes. Here we describe the cell-permeant, lipid-like acridine orange derivative MAO-N3 and use it to assemble high-density, environmentally sensitive (HIDE) probes that selectively label and image the IMM in live cells. MAO-N3 pairs with multiple SPAAC-reactive fluorophores to support HIDE imaging via confocal, Structured Illumination, Single Molecule Localization, and Stimulated Emission Depletion microscopy, all with significantly improved resistance against photobleaching. The HIDE probes generated using MAO-N3 require no genetic manipulations, are non-toxic in model cell lines and primary cardiomyocytes, even under conditions that amplify the effects of mitochondrial toxins, and visualize the IMM for up to 12.5 hours with unprecedented spatial and temporal resolution.

cell biology↗

bioRxiv2022

Dose-dependent nuclear delivery and transcriptional repression with a cell-penetrant MeCP2

Methyl-CpG-binding-protein 2 (MeCP2) is a nuclear protein expressed in all cell types, especially neurons1. Mutations in the MECP2 gene cause Rett syndrome (RTT), an incurable neurological disorder that disproportionately affects young girls2. Strategies to restore MeCP2 expression phenotypically reverse RTT-like symptoms in male and female MeCP2-deficient mice3-5, suggesting that direct nuclear delivery of functional MeCP2 could restore MeCP2 activity. We report that ZF-tMeCP2, a conjugate of MeCP2({Delta}aa13-71, 313-484)6 and the cell-permeant mini-protein ZF5.37-11, both binds DNA in a methylation-dependent manner and reaches the nucleus of model cell lines intact at concentrations above 700 nM. When delivered to live cells, ZF-tMeCP2 engages the NCoR/SMRT co-repressor complex and selectively represses transcription from methylated promoters. Efficient nuclear delivery of ZF-tMeCP2 relies on a unique endosomal escape portal provided by HOPS-dependent endosomal fusion. The Tat conjugate of MeCP2 (Tat-tMeCP2), evaluated for comparison, is degraded within the nucleus, is not selective for methylated promoters, and trafficks in a HOPS-independent manner. These results support the feasibility of a HOPS-dependent portal for delivering functional macromolecules to the cell interior using the cell-penetrant mini-protein ZF5.3. Such a strategy could broaden the impact of multiple families of protein-derived therapeutics.

biochemistry↗

bioRxiv2020

Coiled coil control of diverse EGFR functions

EGFR exhibits biased signaling, whereby growth factor or mutation-dependent changes in receptor conformation and/or dynamics elicit distinct intracellular outcomes. We report that many outcomes associated with activated EGFR are controlled by a two-state coiled coil switch located within the juxtamembrane segment (JM), an essential component of the cytosolic dimer interface. The position of this switch defines the path of endocytic trafficking and whether or not EGFR is degraded within lysosomes. JM coiled coil identity also predicts kinase-independent effects of oncogenic EGFR mutations and clinically relevant tyrosine kinase inhibitors (TKIs) that promote efficient, lysosome-based EGFR degradation. These findings provide a model for biased EGFR signaling, insights into kinase-independent activities of EGFR and clinically relevant TKIs, and identify new strategies for modulating protein lifetime.

biochemistry↗