Biological iron-sulfur clusters: Mechanistic insights from mass spectrometry.

• Iron-sulfur clusters are ubiquitous in life and diverse in function. • Native mass spectrometry provides novel insight into iron-sulfur cluster chemistry. • Cluster-specific Fe/S isotope substitutions confirm mass spectrometric assignments. • Time-resolved native mass spectrometry unravels mechanisms of cluster conversion. Iron-sulfur (FeS) clusters are protein cofactors that are ubiquitous in life, performing a wide range of functions, such as in electron transfer, catalysis and gene regulation. This functional diversity is underpinned by the inherent reactivity of FeS clusters towards redox change and reaction with small molecules such as molecular oxygen and nitric oxide. Such reactivity also presents significant challenges for their study, and difficulties in obtaining sufficient quantities of stable, homogenous FeS protein samples have severely hampered progress in understanding these fascinating proteins. Recently, the application of mass spectrometry, under conditions where the cluster cofactor remains protein-associated, has yielded major new insight, particularly into FeS cluster assembly and the chemistry occurring at the FeS clusters of transcriptional regulators that coordinate the cell's response to changing conditions, such as availability of O 2 and cellular iron status, or the onset of oxidative or nitrosative stress. Here we review this recent progress, highlighting the power of native mass spectrometric approaches for studies of protein cofactors. [ABSTRACT FROM AUTHOR]