Structures and Mechanisms of Protein Remodeling Machines

When a cellular protein has done its job or lost its utility, it should be removed, recycled, or remodeled. These tasks are performed by members of the ubiquitous family of AAA ATPases (ATPases associated with diverse cellular activities) that convert the energy of ATP hydrolysis into mechanical forces that can unfold protein aggregates, degrade unwanted proteins, and remodel protein complexes. To learn how AAA ATPases unfold proteins, Hill, Shen, Sundquist, and colleagues used electron cryomicroscopy to determine structures and elucidate the common mechanisms of several different AAA ATPases in complex with their polypeptide substrates. The team found that each enzyme forms a hexameric ring shaped like a lock washer, with the substrate in the central pore.