Biology subjects

Sharp, K. A.

Publications and source records attributed to Sharp, K. A..

3 recordsLinked to original sources

bioRxiv2026

Biased stochastic motor dynamics drive bidirectional, processive translocation by the AAA+ disaggregase Hsp104.

Protein aggregation disrupts proteostasis and drives neurodegeneration. Hsp104 is a hexameric, ring-shaped AAA+ ATPase that dissolves protein aggregates, yet how hexamers translocate and extract polypeptides trapped in mechanically resistant aggregates remains unclear. Using substrates that recapitulate the physical constraints of aggregates, we establish that Hsp104 is a processive, bidirectional translocase that can dynamically switch direction while threading a single polypeptide. On mechanically restrained substrates and prions, Hsp104 hexamers execute biased stochastic transitions among three conformational states at individual interprotomer interfaces: closed, extended, and a previously unobserved hyperextended form. These transitions follow kinetically favored paths rather than a rigid rotary sequence. The resulting biased stochastic stepping, enabled by the conformational plasticity of Hsp104 hexamers, underpins operational adaptability and redefines the functional logic of AAA+ motors.

biochemistry↗

bioRxiv2021

Evidence for a Nuclear Role for Drosophila Dlg as a Regulator of the NURF Complex

Scrib, Dlg, and Lgl are basolateral regulators of epithelial polarity and tumor suppressors whose molecular mechanisms of action remain unclear. We used proximity biotinylation to identify proteins localized near Dlg in the Drosophila wing imaginal disc epithelium. In addition to expected membrane- and cytoskeleton-associated protein classes, nuclear proteins were prevalent in the resulting mass spectrometry data set, including all four members of the NURF chromatin remodeling complex. Subcellular fractionation demonstrated a nuclear pool of Dlg and proximity ligation confirmed its position near the NURF complex. Genetic analysis showed that NURF activity is also required for the overgrowth of dlg tumors, and this growth suppression correlated with a reduction in Hippo pathway gene expression. Together, these data suggest a nuclear role for Dlg in regulating chromatin and transcription through a more direct mechanism than previously thought. Highlight SummaryProximity proteomics is used as an entry point towards identifying partners of the polarity-regulating tumor suppressor Dlg. A nuclear pool of the protein associated with NURF chromatin remodelers is revealed, along with evidence of functional interactions during growth regulation.

cell biology↗

bioRxiv2018

Simulations and Electrostatic Analysis Suggest an Active Role for DNA Conformational Changes During Genome Packaging by Bacteriophages

Motors that move DNA, or that move along DNA, play essential roles in DNA replication, transcription, recombination, and chromosome segregation. The mechanisms by which these DNA translocases operate remain largely unknown. Some double-stranded DNA (dsDNA) viruses use an ATP-dependent motor to drive DNA into preformed capsids. These include several human pathogens, as well as dsDNA bacteriophages - viruses that infect bacteria. We previously proposed that DNA is not a passive substrate of bacteriophage packaging motors but is, instead, an active component of the machinery. Computational studies on dsDNA in the channel of viral portal proteins reported here reveal DNA conformational changes consistent with that hypothesis. dsDNA becomes longer (\"stretched\") in regions of high negative electrostatic potential, and shorter (\"scrunched\") in regions of high positive potential. These results suggest a mechanism that couples the energy released by ATP hydrolysis to DNA translocation: The chemical cycle of ATP binding, hydrolysis and product release drives a cycle of protein conformational changes. This produces changes in the electrostatic potential in the channel through the portal, and these drive cyclic changes in the length of dsDNA. The DNA motions are captured by a coordinated protein-DNA grip-and-release cycle to produce DNA translocation. In short, the ATPase, portal and dsDNA work synergistically to promote genome packaging.

biophysics↗