J. Am. Chem. Soc. 137, 15358–15361 (2015)

Credit: J. AM. CHEM. SOC.

Gold-thiol bonds form the basis of many nanotechnology and materials platforms, with existing characterization suggesting that the strengths of the bonds vary widely depending on local conditions. Wei et al. now use single-molecule force spectroscopy and X-ray crystallography to examine these interactions in the context of a recently discovered gold-binding protein, GolB. For the force spectroscopy studies, the authors created a chimera containing four repeats of GolB coupled with a fast-folding β-hairpin reporter. When GolB was in the apo form, the forces needed to unfold it were below the instrumental detection limit. Upon addition of gold ions, peaks were observed corresponding to forces of 165 ± 55 pN, much lower than seen in non-biological contexts but similar to results from previous studies on the strengths of proteinaceous iron-sulfur bonds. Though GolB is functionally able to discriminate gold from copper, the forces needed to unfold Cu-loaded GolB were similar to those for Au-loaded species, suggesting that GolB's specificity is not linked to the strength of binding. The long S-Au bonds observed in the GolB crystal structure, in which the chelation strength of the thiolates is likely attenuated by neighboring groups, provide a rationale for the low mechanical strength. The authors hypothesize that these weak bonds are what enable GolB to serve as a gold-specific chaperone.