Biology subjects

Kaur, U.

Publications and source records attributed to Kaur, U..

3 recordsLinked to original sources

bioRxiv2026

ATP-dependent reorientation on a nucleosome primes INO80 for DNA translocation

ATP-dependent chromatin remodeling enzymes play central roles in genome regulation by mobilizing nucleosomes. All remodelers except for one, position their core ATPase at an internal nucleosome location, superhelical location (SHL) 2, and translocate DNA from this site to alter nucleosome conformation. The exception, the remodeler INO80, positions its core ATPase, Ino80, near the DNA exit/entry site, SHL -6. This major architectural difference has raised the question of whether INO80 acts by a fundamentally different mechanism from other remodelers. Here, using cryogenic electron microscopy we capture a new conformation of INO80 that is substantially enriched upon ATP hydrolysis and has Ino80 positioned at an internal nucleosomal location. Comprehensive conformational landscape analysis further uncovers an ATP hydrolysis dependent continuum of additional INO80 conformational states on a nucleosome that were not previously detected. Our studies provide compelling evidence to support a model where INO80 initially engages nucleosomes near SHL -6, followed by a dramatic ATP hydrolysis dependent ~180{degrees} reorientation around the nucleosome to place its Ino80 near SHL -2 from where DNA is translocated. INO80s unique reorientation has broad implications for understanding how ATP-dependent steps that precede nucleosome mobilization can increase the fidelity of remodeling by being responsive to nucleosomal cues.

biophysics↗

bioRxiv2024

ATP-dependent remodeling of chromatin condensates uncovers distinct mesoscale effects of two remodelers

ATP-dependent chromatin remodeling enzymes mobilize nucleosomes, but how such mobilization affects chromatin condensation is unclear. Here, we investigate effects of two major remodelers, ACF and RSC using chromatin condensates and single-molecule footprinting. We find that both remodelers inhibit the formation of condensed chromatin. However, the remodelers have distinct effects on pre-formed chromatin condensates. ACF spaces nucleosomes without de-condensing the chromatin, explaining how ACF maintains nucleosome organization in transcriptionally repressed genomic regions. In contrast, RSC catalyzes ATP-dependent de-condensation of chromatin. Surprisingly, RSC also drives micron-scale movements of entire condensates. These newly uncovered activities of RSC explain its central role in transcriptional activation. The biological importance of remodelers may thus reflect both their effects on nucleosome mobilization and the corresponding consequences on chromatin dynamics at the mesoscale.

biochemistry↗

bioRxiv2023

The conformational landscape of a serpin N-terminal subdomain facilitates folding and in-cell quality control

Many multi-domain proteins including the serpin family of serine protease inhibitors contain non-sequential domains composed of regions that are far apart in sequence. Because proteins are translated vectorially from N-to C-terminus, such domains pose a particular challenge: how to balance the conformational lability necessary to form productive interactions between early and late translated regions while avoiding aggregation. This balance is mediated by the protein sequence properties and the interactions of the folding protein with the cellular quality control machinery. For serpins, particularly 1-antitrypsin (AAT), mutations often lead to polymer accumulation in cells and consequent disease suggesting that the lability/aggregation balance is especially precarious. Therefore, we investigated the properties of progressively longer AAT N-terminal fragments in solution and in cells. The N-terminal subdomain, residues 1-190 (AAT190), is monomeric in solution and efficiently degraded in cells. More y-rich fragments, 1-290 and 1-323, form small oligomers in solution, but are still efficiently degraded, and even the polymerization promoting Siiyama (S53F) mutation did not significantly affect fragment degradation. In vitro, the AAT190 region is among the last regions incorporated into the final structure. Hydrogen-deuterium exchange mass spectrometry and enhanced sampling molecular dynamics simulations show that AAT190 has a broad, dynamic conformational ensemble that helps protect one particularly aggregation prone y-strand from solvent. These AAT190 dynamics result in transient exposure of sequences that are buried in folded, full-length AAT, which may provide important recognition sites for the cellular quality control machinery and facilitate degradation and, under favorable conditions, reduce the likelihood of polymerization.

biophysics↗