Biology subjects

Higashi, T. L.

Publications and source records attributed to Higashi, T. L..

3 recordsLinked to original sources

bioRxiv2026

DNA entry into the cohesin ring through the kleisin N-gate

The ring-shaped cohesin complex topologically entraps two DNAs to establish sister chromatid cohesion, a prerequisite for faithful chromosome segregation during cell divisions. How DNA enters the cohesin ring remains incompletely understood. Both the interface between Psm3Smc3 and the Rad21Scc1 N-terminus - the N-gate - and the SMC hinge interface - the hinge gate - can open in vitro to entrap DNA. Here, we combine biochemical with in vivo functional assays in the fission yeast S. pombe to probe the DNA entry mechanism. Locking the hinge gate does not interfere with cohesin loader-and ATP hydrolysis-dependent DNA entrapment. Conversely, cohesin with a tightly locked N-gate entraps DNA in vitro but does not load onto chromatin or establish sister chromatid cohesion in vivo. The cohesin ATPase is functionally coupled to N-gate, but not hinge-gate, opening. Our results put forward the N-gate as the primary DNA entry gate into the cohesin ring.

molecular biology↗

bioRxiv2021

A Brownian ratchet model for DNA loop extrusion by the cohesin complex

The cohesin complex topologically encircles DNA to promote sister chromatid cohesion. Alternatively cohesin extrudes DNA loops, thought to reflect chromatin domain formation. Here, we propose a structure-based model explaining both activities, supported by biochemical experiments. ATP and DNA binding to cohesin promote conformational changes that guide DNA through a kleisin gate into a DNA gripping state. Two HEAT-repeat DNA binding modules, associated with cohesins heads and hinge, are now juxtaposed. ATP hydrolysis disassembles the gripping state, allowing unidirectional hinge module movement to complete topological DNA entry. Without initial kleisin gate passage, biased hinge module motion during gripping state resolution creates a Brownian ratchet that drives loop extrusion. Molecular-mechanical simulations of gripping state formation and resolution cycles recapitulate experimentally observed DNA loop extrusion characteristics. Our model extends to asymmetric and symmetric loop extrusion, as well as z-loop formation. Loop extrusion by biased Brownian fluctuations has important implications for chromosomal cohesin function.

biophysics↗

bioRxiv2020

A Structure-Based Mechanism for DNA Entry into the Cohesin Ring

Despite key roles in sister chromatid cohesion and chromosome organization, the mechanism by which cohesin rings are loaded onto DNA is still unknown. Here, we combine biophysical approaches and cryo-EM to visualize a cohesin loading intermediate in which DNA is locked between two gates that lead into the cohesin ring. Building on this structural framework, we design biochemical experiments to establish the order of events during cohesin loading. In an initial step, DNA traverses an N-terminal kleisin gate that is first opened upon ATP binding and then closed as the cohesin loader locks the DNA against a shut ATPase gate. ATP hydrolysis leads to ATPase gate opening to complete DNA entry. Whether DNA loading is successful, or rather results in loop extrusion, might be dictated by a conserved kleisin N-terminal tail that guides the DNA through the kleisin gate. Our results establish the molecular basis for cohesin loading onto DNA.

molecular biology↗