Structural maintenance of chromosomes (SMC) complexes shape the genomes of virtually all organisms, but how they function remains incompletely understood. Recent studies in bacteria and eukaryotes have led to a unifying model in which these ring-shaped ATPases act along contiguous DNA segments, processively enlarging DNA loops. In support of this model, single-molecule imaging experiments indicate that Saccharomyces cerevisiae condensin complexes can extrude DNA loops in an ATP-hydrolysis-dependent manner in vitro. Here, using time-resolved high-throughput chromosome conformation capture (Hi-C), we investigate the interplay between ATPase activity of the Bacillus subtilis SMC complex and loop formation in vivo. We show that point mutants in the SMC nucleotide-binding domain that impair but do not eliminate ATPase activity not only exhibit delays in de novo loop formation but also have reduced rates of processive loop enlargement. These data provide in vivo evidence that SMC complexes function as loop extruders.

Despite their shared ability to regulate microtubule polymerization dynamics, kinesin-4 motors display dramatically different motility properties ranging from fast processive motility to no movement. Yue et al. demonstrate that for KIF7 and KIF27, altered chemomechanical coupling results in immotile behavior and slow processive movement, respectively.

Myosin active site elements (i.e., switch‐1) bind both ATP and a divalent metal to coordinate ATP hydrolysis. ATP hydrolysis at the active site is linked via allosteric communication to the actin polymer binding site and lever arm movement, thus coupling the free energy of ATP hydrolysis to force generation. How active site motifs are functionally linked to actin binding and the power stroke is still poorly understood. We hypothesize that destabilizing switch‐1 movement at the active site will negatively affect the tight coupling of the ATPase catalytic cycle to force production. Using a metal‐switch system, we tested the effect of interfering with switch‐1 coordination of the divalent metal cofactor on force generation. We found that while ATPase activity increased, motility was inhibited. Our results demonstrate that a single atom change that affects the switch‐1 interaction with the divalent metal directly affects actin binding and productive force generation. Even slight modification of the switch‐1 divalent metal coordination can decouple ATP hydrolysis from motility. Switch‐1 movement is therefore critical for both structural communication with the actin binding site, as well as coupling the energy of ATP hydrolysis to force generation.

Chromokinesins NOD and KID have similar DNA binding domains and functions during cell division, while their motor domain sequences show significant variations. It has been unclear whether these motors have similar structure, chemistry, and microtubule interactions necessary to follow a similar mechanism of force mediation. We used biochemical rate measurements, cosedimentation, and structural analysis to investigate the ATPase mechanisms of the NOD and KID core domains. These experiments and analysis revealed that NOD and KID have different ATPase mechanisms, microtubule interactions, and catalytic domain structures. The ATPase cycles of NOD and KID have different rate limiting steps. The ATPase rate of NOD was robustly stimulated by microtubules albeit its microtubule affinity was weakened in all nucleotide bound states. KID bound microtubules tightly in all nucleotide states and remained associated with the microtubule for more than 100 cycles of ATP hydrolysis before dissociating. The structure of KID was most similar to conventional kinesin (KIF5). Key differences in the microtubule binding region and allosteric communication pathway between KID and NOD are consistent with our biochemical data. Our results support the model that NOD and KID utilize distinct mechanistic pathways to achieve the same function during cell division..

Chromokinesins NOD and KID have similar DNA binding domains and functions during cell division, while their motor domain sequences show significant variations. It has beenunclear whether these motors have similar structure, chemistry, and microtubule interactions necessary to follow a similar mechanism of force mediation. We used biochemical rate measurements, cosedimentation, and structural analysis to investigate the ATPase mechanisms of the NOD and KID core domains. These experiments and analysis revealed that NOD and KID have different ATPase mechanisms, microtubule interactions, and catalytic domain structures. The ATPase cycles of NOD and KID have different rate limiting steps. The ATPase rate of NOD was robustly stimulated by microtubules albeit its microtubule affinity was weakened in all nucleotide bound states. KID bound microtubules tightly in all nucleotide states and remained associated with the microtubule for more than 100 cycles of ATP hydrolysis before dissociating. The structure of KID was most similar to conventional kinesin (KIF5). Key differences in the microtubule binding region and allosteric communication pathway between KID and NOD are consistent with our biochemical data. Our results support the model that NOD and KID utilize distinct mechanistic pathways to achieve the same function during cell division.