Forced extraction of targeted components from complex macromolecular assemblies.

When individual protein components of supramolecular complexes are required for assembly, determining whether they play additional structural or functional roles can be difficult. Removing a protein from the complex after assembly can circumvent this problem. Here, we show that an AAA+ unfoldase/protease can extract an essential assembly protein from the ribosome. Specifically, Mg(2+) depletion allowed ClpXP to remove an ssrA-tagged variant of ribosomal protein L22 from the 50S subunit of E. coli ribosomes without disrupting either the structural integrity or hydrodynamic properties of the modified particle. Forced extraction using AAA+ enzymes and targeted component proteins should be broadly applicable to the study of macromolecular complexes.