The Use of Mn(II) Bound to His-tags as Genetically Encodable Spin-Label for Nanometric Distance Determination in Proteins

J Phys Chem Lett. 2016 Mar 17;7(6):1072-6. doi: 10.1021/acs.jpclett.6b00362. Epub 2016 Mar 8.


A genetically encodable paramagnetic spin-label capable of self-assembly from naturally available components would offer a means for studying the in-cell structure and interactions of a protein by electron paramagnetic resonance (EPR). Here, we demonstrate pulse electron-electron double resonance (DEER) measurements on spin-labels consisting of Mn(II) ions coordinated to a sequence of histidines, so-called His-tags, that are ubiquitously added by genetic engineering to facilitate protein purification. Although the affinity of His-tags for Mn(II) was low (800 μM), Mn(II)-bound His-tags yielded readily detectable DEER time traces even at concentrations expected in cells. We were able to determine accurately the distance between two His-tag Mn(II) spin-labels at the ends of a rigid helical polyproline peptide of known structure, as well as at the ends of a completely cell-synthesized 3-helix bundle. This approach not only greatly simplifies the labeling procedure but also represents a first step towards using self-assembling metal spin-labels for in-cell distance measurements.

Publication types

  • Letter
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Electron Spin Resonance Spectroscopy
  • Histidine / chemistry*
  • Manganese / chemistry*
  • Molecular Dynamics Simulation
  • Peptides / chemistry
  • Protein Structure, Tertiary
  • Proteins / chemistry*
  • Spin Labels*


  • Peptides
  • Proteins
  • Spin Labels
  • Manganese
  • Histidine