Sister DNA entrapment between juxtaposed Smc heads and kleisin of the cohesin complex

Cohesin entraps sister DNAs within tripartite rings created by pairwise interactions between Smc1, Smc3, and Scc1. Because Smc1/3 ATPase heads can also interact with each other, cohesin rings have the potential to form a variety of sub-compartments. Using in vivo cysteine cross-linking, we show that when Smc1 and Smc3 ATPases are engaged in the presence of ATP (E heads), cohesin rings generate a “SMC (S) compartment” between hinge and E heads and a “kleisin (K) compartment” between E heads and their associated kleisin subunit. Upon ATP hydrolysis, cohesin’s heads associate in a different mode, in which their signature motifs and their coiled coils are closely juxtaposed (J heads), creating alternative S and K compartments. We show that K compartments of either E or J type can entrap single DNAs, that acetylation of Smc3 during S phase is associated with J heads, and that sister DNAs are entrapped in J-K compartments

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Investigation of Hemicryptophane Host-Guest Binding Energies Using High-Pressure Collision-Induced Dissociation in Combination with RRKM Modeling

International audienceIn advancing host-guest (H-G) chemistry, considerable effort has been spent to synthesize host molecules with specific and well-defined molecular recognition characteristics including selectivity and adjustable affinity. An important step in the process is the characterization of binding strengths of the H-G complexes that is typically performed in solution using NMR or fluorescence. Here, we present a mass spectrometry-based multimodal approach to obtain critical energies of dissociation for two hemicryptophane cages with three biologically-relevant guest molecules. A combination of blackbody infrared radiative dissociation (BIRD) and high-pressure collision induced dissociation (high-pressure CID), along with RRKM modeling, were employed for this purpose. For the two tested hemicryptophane hosts, the cage containing naphthyl linkages exhibited stronger interactions than the cage bearing phenyl linkages. For both cages, the order of guest stability is: choline > acetylcholine > betaine. The information obtained by these types of mass spectrometric studies can provide new insight into the structural features that most influence the stability of H-G pairs, thereby providing guidance for future syntheses