Dara Dowlatshahi

All Publications

• Exploring Transient States of PAmKate to Enable Improved Cryogenic Single-Molecule Imaging. Journal of the American Chemical Society Perez, D., Dowlatshahi, D. P., Azaldegui, C. A., Ansell, T. B., Dahlberg, P. D., Moerner, W. E. 2024

  Abstract

  Super-resolved cryogenic correlative light and electron microscopy is a powerful approach which combines the single-molecule specificity and sensitivity of fluorescence imaging with the nanoscale resolution of cryogenic electron tomography. Key to this method is active control over the emissive state of fluorescent labels to ensure sufficient sparsity to localize individual emitters. Recent work has identified fluorescent proteins (FPs) that photoactivate or photoswitch efficiently at cryogenic temperatures, but long on-times due to reduced quantum yield of photobleaching remain a challenge for imaging structures with a high density of localizations. In this work, we explore the photophysical properties of the red photoactivatable FP PAmKate and identify a 2-color process leading to enhanced turn-off of active emitters, improving localization rate. Specifically, after excitation of ground state molecules, we find that a transient state forms with a lifetime of 2 ms under cryogenic conditions, which can be bleached by exposure to a second wavelength. We measure the response of the transient state to different wavelengths, demonstrate how this mechanism can be used to improve imaging, and provide a blueprint for the study of other FPs at cryogenic temperatures.

  View details for DOI 10.1021/jacs.4c05632

  View details for PubMedID 39388715

• Exploring transient states of PAmKate to enable improved cryogenic single-molecule imaging. bioRxiv : the preprint server for biology Perez, D., Dowlatshahi, D. P., Azaldegui, C. A., Dahlberg, P. D., Moerner, W. E. 2024

  Abstract

  Super-resolved cryogenic correlative light and electron microscopy is a powerful approach which combines the single-molecule specificity and sensitivity of fluorescence imaging with the nano-scale resolution of cryogenic electron tomography. Key to this method is active control over the emissive state of fluorescent labels to ensure sufficient sparsity to localize individual emitters. Recent work has identified fluorescent proteins (FPs) which photoactivate or photoswitch efficiently at cryogenic temperatures, but long on-times due to reduced quantum yield of photobleaching remains a challenge for imaging structures with a high density of localizations. In this work, we explore the photophysical properties of the red photoactivatable FP PAmKate and identify a 2-color process leading to enhanced turn-off of active emitters, improving localization rate. Specifically, after excitation of ground state molecules, we find a transient state forms with a lifetime of ~2 ms which can be bleached by exposure to a second wavelength. We measure the response of the transient state to different wavelengths, demonstrate how this mechanism can be used to improve imaging, and provide a blueprint for study of other FPs at cryogenic temperatures.

  View details for DOI 10.1101/2024.04.24.590965

  View details for PubMedID 38712218

  View details for PubMedCentralID PMC11071506

• ALIX Is a Lys63-Specific Polyubiquitin Binding Protein that Functions in Retrovirus Budding DEVELOPMENTAL CELL Dowlatshahi, D. P., Sandrin, V., Vivona, S., Shaler, T. A., Kaiser, S. E., Melandri, F., Sundquist, W. I., Kopito, R. R. 2012; 23 (6): 1247-1254

  Abstract

  The diversity of ubiquitin (Ub)-dependent signaling is attributed to the ability of this small protein to form different types of covalently linked polyUb chains and to the existence of Ub binding proteins that interpret this molecular syntax. We used affinity capture/mass spectrometry to identify ALIX, a component of the ESCRT pathway, as a Ub binding protein. We report that the V domain of ALIX binds directly and selectively to K63-linked polyUb chains, exhibiting a strong preference for chains composed of more than three Ub. Sequence analysis identified two potential Ub binding sites on a single α-helical surface within the coiled-coil region of the V domain. Mutation of these putative Ub binding sites inhibited polyUb binding to the isolated V domain in vitro and impaired budding of lentiviruses. These data reveal an important role for K63 polyUb binding by ALIX in retroviral release.

  View details for DOI 10.1016/j.devcel.2012.10.023

  View details for Web of Science ID 000312429200020

  View details for PubMedID 23201121

  View details for PubMedCentralID PMC3522770

• An AMPK-FOXO pathway mediates longevity induced by a novel method of dietary restriction in C-elegans CURRENT BIOLOGY Greer, E. L., Dowlatshahi, D., Banko, M. R., Villen, J., Hoang, K., Blanchard, D., Gygi, S. P., Brunet, A. 2007; 17 (19): 1646-1656

  Abstract

  Dietary restriction (DR) is the most effective environmental intervention to extend lifespan in a wide range of species. However, the molecular mechanisms underlying the benefits of DR on longevity are still poorly characterized. AMP-activated protein kinase (AMPK) is activated by a decrease in energy levels, raising the possibility that AMPK might mediate lifespan extension by DR.By using a novel DR assay that we developed and validated in C. elegans, we find that AMPK is required for this DR method to extend lifespan and delay age-dependent decline. We find that AMPK exerts its effects in part via the FOXO transcription factor DAF-16. FOXO/DAF-16 is necessary for the beneficial effects of this DR method on lifespan. Expression of an active version of AMPK in worms increases stress resistance and extends longevity in a FOXO/DAF-16-dependent manner. Lastly, we find that AMPK activates FOXO/DAF-16-dependent transcription and phosphorylates FOXO/DAF-16 at previously unidentified sites, suggesting a possible direct mechanism of regulation of FOXO/DAF-16 by AMPK.Our study shows that an energy-sensing AMPK-FOXO pathway mediates the lifespan extension induced by a novel method of dietary restriction in C. elegans.

  View details for DOI 10.1016/j.cub.2007.08.047

  View details for Web of Science ID 000250125200023

  View details for PubMedID 17900900

  View details for PubMedCentralID PMC2185793