Sensitive probes of protein structure and dynamics in well-controlled environments: combining mass spectrometry with fluorescence spectroscopy.

Combining the selectivity of mass spectrometry (MS) with laser-induced fluorescence (LIF) presents a promising route to probe the intrinsic conformation, stability and dynamics of biological macromolecules. However, applications to proteins are in their infancy. Recent advances include the realization of Förster (fluorescence) resonance energy transfer (FRET) to provide nm-range distance constraints in de-solvated proteins, and measurement of dynamic fluorescence quenching rates to assess shorter-range interactions in peptides and Trp-cage. Temperature-dependent experiments employing FRET and dynamic quenching as conformational probes enable determination of enthalpy and entropy of conformational change in de-solvated biomolecules. These developments show the feasibility of using MS-LIF to dissect complex molecular interactions. For example, MS-LIF of protein-ligand complexes and partially hydrated proteins will better elucidate the energetics of specific binding interactions and the role of the solvent in protein structure and folding.