Atomic force microscopy captures length phenotypes in single proteins

摘要

We use single-protein atomic force micros- copy techniques to detect length phenotypes in an Ig module. To gain amino acid resolution, we amplify the mechanical features of a single module by engineering polyproteins com- posed of up to 12 identical repeats. We show that on mechan- ical unfolding, mutant polyproteins containing five extra glyqine residues added to the folded core of the module extend 20 A per module farther than the wild-type polyproteins. By contrast, similar insertions near the N or C termini have no effect. Hence, our atomic force microscopy measurements readily discriminate the location of the insert and measure its size with a resolution similar to that of NMR and x-ray crystallography.