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Eur. J. Mass Spectrom. 3, 453 - 459 (1997) |
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Electrospray ionization mass spectrometry temperature effects on metal ion:protein stoichiometries and metal-induced conformational changes in calmodulin | ||
Timothy D. Veenstra |
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ABSTRACT: | ||
The calcium ion (Ca2+) binding stoichiometry required to induce a complete, tertiary conformational change of calmodulin is still disputed. Several studies have indicated that this occurs upon the uptake of only two Ca2+; more recent reports, however, indicate that four Ca2+ are required. We used electrospray ionization (ESI) mass spectrometry under standard ESI conditions (i.e. high temperature, organic co-solvent) to identify definitively the Ca2+ stoichiometry required to induce a conformational change in the protein, and we demonstrate that four Ca2+ are needed. We then undertook a comparative study on the Ca2+-binding of calmodulin using a lower ESI source temperature. Under these conditions we can detect Ca2+-saturated calmodulin at much lower Ca2+ to protein molar ratios than those observed using typical ESI conditions. This latter observation more closely reflects the solution-phase conditions that are noted using aqueous solution-based spectroscopies to study proteinmetal binding. | ||
Keywords: Low temperature, electrospray ionization mass spectrometry, calmodulin, calcium, conformation. |
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