Methods to identify and characterize iron–sulfur oligopeptides in water

Iron–sulfur clusters are ubiquitous cofactors that mediate central biological processes. However, despite their long history, these metallocofactors remain challenging to investigate when coordinated to small (≤ six amino acids) oligopeptides in aqueous solution. In addition to being often unstable in vitro, iron–sulfur clusters can be found in a wide variety of forms with varied characteristics, which makes it difficult to easily discern what is in solution. This difficulty is compounded by the dynamics of iron–sulfur peptides, which frequently coordinate multiple types of clusters simultaneously. To aid investigations of such complex samples, a summary of data from multiple techniques used to characterize both iron–sulfur proteins and peptides is provided. Although not all spectroscopic techniques are equally insightful, it is possible to use several, readily available methods to gain insight into the complex composition of aqueous solutions of iron–sulfur peptides.