| Abstract
| - The behavior of macromolecular systems at differenttemperatures is often crucial to their biological activity andfunction. While heat-induced changes of individual proteins are readily monitored by a number of spectroscopicmethods, changes in noncovalent complexes of biomolecules are more challenging to interpret. Nanoelectrospray mass spectrometry is becoming increasingly powerful in the study of large noncovalent complexes, andhere we describe the design, characterization, and application of a novel probe that allows the thermocontrolof the solution in the electrospray capillary. The transitiontemperature for the unfolding of the protein lysozyme isreadily obtained and correlates closely with that measuredby fluorescence spectroscopy, thereby demonstrating thevalidity of this approach. We apply this technique to thestudy of the 200-kDa complex of the small heat shockprotein TaHSP16.9, revealing both its dissociation intosuboligomeric species and an increase in its size andpolydispersity at elevated temperatures. In contrast, gas-phase activation of this complex is also carried out andyields a dissociation pathway fundamentally different fromthat observed for thermal activation in solution. As such,this probe allows the study of the reversible heat-inducedchanges of noncovalent complexes in a biologically relevant manner.
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