Inducing α‐Helicity in Peptides by Silver Coordination to Cysteine.

Short peptide sequences consisting of two cysteine residues separated by three other amino acids display complete change from random coil to α‐helical secondary structure in response to addition of Ag+ ions. The folded CXXXC/Ag+ complex involves formation of multinuclear Ag+ species and is stable in a wide pH range from below 3 to above 8. The complex is stable through reversed‐phase HPLC separation as well as towards a physiological level of chloride ions, based on far‐UV circular dichroism spectroscopy. In electrospray MS under acidic conditions a peptide dimer with four Ag+ ions bound was observed, and modelling based on potentiometric experiments supported this to be the dominating complex at neutral pH together with a peptide dimer with 3 Ag+ and one proton at lower pH. The complex was demonstrated to work as a N‐terminal nucleation site for inducing α‐helicity into longer peptides. This type of silver‐mediated peptide assembly and folding may be of more general use for stabilizing not only peptide folding but also for controlling oligomerization even under acidic conditions. [ABSTRACT FROM AUTHOR]