Mutant chaperonin proteins: new tools for nanotechnology

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Much effort has gone into finding peptides that bind potentially useful nanoparticles, butrelatively little effort has focused on the scaffolds that organize these peptides into usefulnanostructures. Chaperonins are protein complexes with 14–18 protein subunits thatself-assemble into double-ring complexes and function as scaffolds for peptides or aminoacids that bind metallic and semiconductor quantum dots. The utility of chaperonins asscaffolds depends on their structure and their ability to self-assemble into double-rings andhigher-order structures, such as filaments and two-dimensional arrays. To betterunderstand the structure of chaperonins, we constructed a model of a group II chaperoninand, based on this model, genetically constructed five mutant subunits with significantdeletions. We expressed these mutants as recombinant proteins and observed by nativepolyacrylamide gel electrophoresis (PAGE) and transmission electron microscopy (TEM)that they all self-assembled into double rings. Our model predicted and TEM confirmedthat these deletions did not significantly change the 17 nm diameter of the wild-type doublerings, but decreased their height and opened their central cavities. Four of the fivemutants formed higher-order structures: chains of rings, bundles of chains orfilaments, and two-dimensional arrays, which we suggest can be useful nanostructures.