Biology subjects

Mears, J. A.

Publications and source records attributed to Mears, J. A..

4 recordsLinked to original sources

bioRxiv2024

The Structure of the Drp1 Lattice on Membrane

Mitochondrial health relies on the membrane fission mediated by dynamin-related protein 1 (Drp1). Previous structural studies of Drp1 on remodeled membranes were hampered by heterogeneity, leaving a critical gap in the understanding of the mitochondrial fission mechanisms. Here we present a cryo-electron microscopy structure of full-length human Drp1 decorated on membrane tubules. Using the reconstruction of average subtracted tubular regions (RASTR) technique, we report that Drp1 forms a locally ordered lattice along the tubule without global helical symmetry. The filaments in the lattice are similar to dynamin rungs with conserved stalk interactions. Adjacent filaments are connected by GTPase domain interactions in a novel stacked conformation. We identified two states of the Drp1 lattice among the heterogenous dataset representing conformational changes around hinge 1. Additionally, we observed contact between Drp1 and membrane that can be assigned to the variable domain sequence. Together these structures revealed a putative mechanism by which Drp1 constricts mitochondria membranes in a stepwise, "ratchet" manner. SUMMARYThis study provides new insights into the structure of Drp1 on lipid membranes. A locally ordered Drp1 lattice structure is solved and reveals intermolecular contacts and conformational rearrangements that suggest a mechanism for constriction of mitochondrial membranes.

biochemistry↗

bioRxiv2023

Structural Basis for Regulated Assembly of the Mitochondrial Fission GTPase Drp1

Mitochondrial fission is crucial for distributing cellular energy throughout cells and for isolating damaged regions of the organelle that are targeted for degradation. This multistep process is initiated by the enhanced recruitment and oligomerization of dynamin-related protein 1 (Drp1) at the surface of mitochondria. As such, Drp1 is essential for inducing mitochondrial division in mammalian cells, and homologous proteins are found in all eukaryotes. De novo missense mutations in the Drp1 gene, DNM1L, are associated with severe neurodevelopmental diseases in patients, and no effective treatments are available. As a member of the dynamin superfamily of proteins (DSPs), controlled Drp1 self-assembly into large helical polymers stimulates its GTPase activity to promote membrane constriction. Still, little is known about the regulatory mechanisms that determine when and where Drp1 self-assembles, and proper mitochondrial dynamics requires correct spatial and temporal assembly of the fission machinery. Here we present a cryo-EM structure of a full-length, native Drp1 dimer in an auto-inhibited state. This dimer reveals two key conformational rearrangements that must be unlocked through intermolecular interactions to achieve the assembly competent state previously observed in crystal and filament structures. Specifically, the G domain is closed against the stalk domain and occludes intermolecular interactions necessary for self-assembly beyond a dimer. Similarly, adjacent stalks in the dimer form a more continuous interface that further occludes conserved intermolecular contact sites. This structural insight provides a novel mechanism for regulated self-assembly of the mitochondrial fission machinery.

cell biology↗

bioRxiv2021

Horizontal mitochondrial transfer from the microenvironment increases glioblastoma tumorigenicity

While dynamic microenvironmental interactions drive tumor growth and therapeutic resistance, the underlying direct cell-cell communication mechanisms remain poorly understood. We identified horizontal mitochondrial transfer as a mechanism that enhances tumorigenesis in glioblastoma. This transfer occurs primarily from brain-resident cells, including astrocytes, and can be appreciated in vitro and in vivo through intercellular connections between GBM cells and non-malignant host cells. The acquisition of astrocyte mitochondria drives an overall enhancement of mitochondrial membrane potential and metabolic capacity, while increasing glioblastoma cell self-renewal and tumor-initiating capacity. Collectively, our findings demonstrate that mitochondrial transfer augments the tumorigenic capacity of glioblastoma cells and reveals a previously unknown cell-cell communication mechanism that drives tumor growth. One-Sentence SummaryMitochondrial transfer from astrocytes to glioblastoma alters metabolic profile and enhances the tumor-initiation capacity.

cancer biology↗

bioRxiv2018

PTBP2-dependent alternative splicing regulates protein transport and mitochondria morphology in post-meiotic germ cells.

The RNA binding protein PTBP2 (polypyrimidine tract binding protein 2) is a key regulator of tissue-specific alternative RNA splicing. In the testis, PTBP2 is expressed in meiotic and post-meiotic germ cells (spermatocytes and spermatids, respectively). In these cells, PTBP2 is required for proper alternative mRNA splicing for over 200 genes, disproportionately affecting genes encoding proteins involved in protein trafficking via transport vesicles. In this study, we used electron microscopy to test the hypothesis that protein trafficking is impaired in the absence of PTBP2, and to further investigate why spermatogenesis abruptly ceases in PTBP2-deficienct spermatids. Ultrastructural analysis shows that protein trafficking in spermatids is aberrant in the absence of PTBP2. Unexpectedly, we also found that mitochondria morphology and number are significantly altered in PTBP2-deficient spermatids, consistent with increased mitochondria fission. Furthermore, we show that genes with key roles in mitochondria dynamics and function are post-transcriptionally regulated by PTBP2 and in different stages of spermatogenesis. Collectively, the data provide ultrastructural evidence that alternative splicing regulation by PTBP2 during spermatogenesis is critical for proper regulation of protein trafficking and mitochondria morphology.

developmental biology↗