Questions about Cohesin - what does the ATPase domain do, and any suggested PDBs to look at?

Question

I've been reading about cohesin lately, and I'm confused about the head subunit interactions. I've read a few papers, and also found this nice figure from wiki that demonstrates the crux of my question (note: SMC here corresponds to Cohesin, or am I mistaken? I'm pretty sure this is correct, or pretty much correct):

From reading around, I'm aware generally the head subunit is an ATPase, yet from this diagram (and from the typical putative "use" of Cohesin in TAD maintenance), I'm not sure what exactly is the ATPase motif so useful for, it seems that the ATP is sort of "glueing" the the two head domains together, but that seems opposite of what ATPase would typically do, ie catalyze ATP -> ADP. This makes me think I'm just misunderstanding something, and wondering what is the function of the Walker A/B ATPase motif.

Also, I'm wondering if there are any nice PDB files that show a cohesin loop, or elsewise are generally the most instructive about Cohesin. I've searched through a few, but would like more informed advice about some good structures, and maybe why they are nice.

Answer 1

This article :

Prakash Arumugam, Stephan Gruber, Koichi Tanaka, Christian H. Haering, Karl Mechtler, Kim Nasmyth, "ATP Hydrolysis Is Required for Cohesin's Association with Chromosomes", Current Biology, Volume 13, Issue 22, 2003,

at

https://www.sciencedirect.com/science/article/pii/S0960982203008042

Their conclusion is:

"Conclusions: Cohesin complexes whose heads have been connected by Scc1 must hydrolyze ATP in order to associate stably with chromosomes. If chromosomal association is mediated by the topological entrapment of DNA inside cohesin's ring, then ATP hydrolysis may be responsible for creating a gate through which DNA can enter. We suggest that ATP hydrolysis drives the temporary disconnection of Scc1 from Smc heads that are needed for DNA entrapment and that this process is promoted by Scc2/4."