Direct measurement of the Mn(II) hydration state in metal complexes and metalloproteins through 17O NMR line widths

J Am Chem Soc. 2013 Dec 11;135(49):18600-8. doi: 10.1021/ja4094132. Epub 2013 Oct 24.

Abstract

Here we describe a simple method to estimate the inner-sphere hydration state of the Mn(II) ion in coordination complexes and metalloproteins. The line width of bulk H2(17)O is measured in the presence and absence of Mn(II) as a function of temperature, and transverse (17)O relaxivities are calculated. It is demonstrated that the maximum (17)O relaxivity is directly proportional to the number of inner-sphere water ligands (q). Using a combination of literature data and experimental data for 12 Mn(II) complexes, we show that this method provides accurate estimates of q with an uncertainty of ±0.2 water molecules. The method can be implemented on commercial NMR spectrometers working at fields of 7 T and higher. The hydration number can be obtained for micromolar Mn(II) concentrations. We show that the technique can be extended to metalloproteins or complex:protein interactions. For example, Mn(II) binds to the multimetal binding site A on human serum albumin with two inner-sphere water ligands that undergo rapid exchange (1.06 × 10(8) s(-1) at 37 °C). The possibility of extending this technique to other metal ions such as Gd(III) is discussed.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Manganese / chemistry*
  • Metalloproteins / chemistry*
  • Nuclear Magnetic Resonance, Biomolecular / methods*
  • Temperature
  • Water / chemistry*

Substances

  • Metalloproteins
  • Water
  • Manganese