Mn(II) tags for DEER distance measurements in proteins via C-S attachment.

Mn(2+) chelating tags for Mn(2+)-Mn(2+) distance measurements by pulse EPR spectroscopy were developed. They feature a stable C-S conjugation to the protein, high reactivity towards cysteine thiols and short and rigid linkers that can be used in distance measurements with high resolution under reductive conditions. Double electron-electron resonance measurements at 95 GHz on ubiquitin labeled with these tags showed the expected narrow distance distribution.