Chart 1. Schematic representation of the five TagRFP variants (0H, 1H, 2H, 1 + 1H, 2 + 1H) used in this study with different numbers of His₆-tags located at the N- and/or C-terminus and/or at the serine-to-cysteine mutation site (S128C). End-on and side-on oriented TagRFP binding scenarios and the complexation of Ni²⁺:NTA SAMs (for preparation see Scheme S1) by a His₆-tag are shown.