In situ NMR measurement of macromolecule-bound metal ion concentrations
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Many nucleic acids and proteins require divalent metal ions such as Mg2+ and Ca2+ for folding and function. The lipophilic alignment media frequently used as membrane mimetics also bind these divalent metals. Here we demonstrate the use of 31P NMR spectrum of a metal ion chelator (deoxycytidine diphosphate) to measure the bound [Mg2+] and [Ca2+] in situ for several biological model systems at relatively high divalent ion concentrations (1–10 mM). This method represents a general approach to measuring divalent metal ion binding in NMR samples where the amount and type of metal ion added to the system is known.
KeywordsDivalent ion concentration 31P NMR dCDP Bicelles Dickerson dodecamer βγ-Crystallin Ca2+ dependent protein
The authors acknowledge Dr. Philip Dennison for excellent management of the UCI NMR facility and Dr. Beniam Berhane for his help with biomolecular mass spectrometry. We thank Dr. Cassandra Burke and Jan Bierma for assistance with sample preparation. We acknowledge Prof. Juli Feigon for her helpful suggestions. This work was supported by NSF Grant CHE1308231 to RWM.
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