Investigation of structure, dynamics and function of metalloproteins with electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry (ESI MS) has emerged recently as a powerful tool for analyzing many structural and behavioral aspects of metalloproteins in great detail. In this review we discuss recent developments in the field, placing particular emphasis on the unique features of ESI MS that lend themselves to metalloprotein characterization at a variety of levels. Direct mass measurement enables the determination of protein-metal ion binding stoichiometry in solution and metalloprotein higher order structure in the case of multi-subunit proteins. MS techniques have been developed for determining the locations of metal-binding centers, metal oxidation states and reaction intermediates of metal-containing enzymes. Other ESI MS techniques are also discussed, such as protein ion charge state distributions and hydrogen/deuterium exchange studies, which can be used to measure metal binding affinities and to shed light on vital dynamic aspects of the functional properties of metalloproteins endowed by metal binding.