Biology subjects

Le, L. T. M.

Publications and source records attributed to Le, L. T. M..

3 recordsLinked to original sources

bioRxiv2023

Fyn-mediated phosphorylation of Menin disrupts telomere maintenance in stem cells

Telomeres protect chromosome ends and determine the replication potential of dividing cells. The canonical telomere sequence TTAGGG is synthesized by telomerase holoenzyme, which maintains telomere length in proliferative stem cells. Although the core components of telomerase are well-defined, mechanisms of telomerase regulation are still under investigation. We report a novel role for the Src family kinase Fyn, which disrupts telomere maintenance in stem cells by phosphorylating the scaffold protein Menin. We found that Fyn knockdown prevented telomere erosion in human and mouse stem cells, validating the results with four telomere measurement techniques. We show that Fyn phosphorylates Menin at tyrosine 603 (Y603), which increases Menins SUMO1 modification, C-terminal stability, and importantly, its association with the telomerase RNA component (TR). Using mass spectrometry, immunoprecipitation, and immunofluorescence experiments we found that SUMO1-Menin decreases TRs association with telomerase subunit Dyskerin, suggesting that Fyns phosphorylation of Menin induces telomerase subunit mislocalization and may compromise telomerase function at telomeres. Importantly, we find that Fyn inhibition reduces accelerated telomere shortening in human iPSCs harboring mutations for dyskeratosis congenita.

molecular biology↗

bioRxiv2021

Structures of the human peroxisomal fatty acid transporter ABCD1 in a lipid environment

The peroxisomal very long chain fatty acid (VLCFA) transporter ABCD1 is central to cellular fatty acid catabolism and lipid biosynthesis. Its dysfunction underlies toxic cytosolic accumulation of VLCFAs, progressive nervous system demyelination, and neurological impairments including the potentially fatal disease X-linked adrenoleukodystrophy (X-ALD). Molecular details underlying substrate recognition and transport by ABCD1 are poorly understood. Here we determined cryo-EM structures of ABCD1 in phospholipid nanodiscs in a nucleotide bound conformation open to the peroxisomal lumen and an inward facing conformation open to the cytosol at up to 3.5 [A] resolution that reveal key details of its transmembrane cavity and ATP dependent conformational transitions. We identify structural elements distinguishing ABCD1 from its closest homologs and show that coenzyme A (CoA) esters of VLCFAs modulate ABCD1 activity in a species dependent manner. Together, our data support a transport mechanism where only the CoA moieties of VLCFA-CoAs enter the hydrophilic transmembrane cavity while the acyl chains extend out into the surrounding membrane bilayer, help rationalize disease causing mutations, and provide a framework for ABCD1 targeted structure-based drug design.

biochemistry↗

bioRxiv2021

Cryo-EM structure of lipid embedded human ABCA7 at 3.6 &Aring resolution

Phospholipid extrusion by ABC subfamily A (ABCA) exporters is central to cellular physiology, although the specifics of the underlying substrate interactions and transport mechanisms remain poorly resolved at the molecular level. Here we report cryo-EM structures of lipid-embedded human ABCA7 in an open state and a nucleotide-bound, closed state at resolutions between 3.6-4.0 [A]. The former reveals an ordered patch of bilayer lipids traversing the transmembrane domain (TMD), while the latter reveals a lipid-free, closed TMD with a small extracellular opening. These structures offer a structural framework for both substrate entry and exit from the ABCA7 TMD and highlight conserved rigid-body motions that underlie the associated conformational transitions. Combined with functional analysis and molecular dynamics (MD) simulations, our data also shed light on lipid partitioning into the ABCA7 TMD and localized membrane perturbations that underlie ABCA7 function and have broader implications for other ABCA family transporters.

biophysics↗