Knitting and snipping: chaperones in β-helix folding

Hallmarks of proteins containing beta-helices are their increased stability and rigidity and their aggregation prone folding pathways. While parallel p-helices fold independently, the folding and assembly of many triple beta-helices depends on a registration signal in order to adopt the correct three-dimensional structure. In some cases this is a mere trimerization domain, in others specialized chaperones are required. Recently, the crystal structures of two classes of intramolecular chaperones of p-helical proteins have been determined. Both mediate the assembly of large tailspike proteins and release themselves after maturation; however, they differ substantially in their structure and autoproteolytic release mechanisms.