Fig. 3: Ni^II-MncA structure indicates non-cognate metal is also kinetically trapped.

a Ribbon representation of crystal structure of (Ni^II)₂MncA at 1.6 Å resolution showing characteristic bi-cupin fold and metal sites (boxed) modelled from residue 39 of the full protein sequence including signal peptide which is absent from the expressed protein (data collection and refinement statistics shown in Supplementary Table 3). Amino-terminal domain (pink), carboxy-terminal domain (blue) from residue 238 (in the full sequence). b, c Cross sections of solvent accessibility surfaces (modelled at 1.1 Å solvent radius to encompass dynamics) surrounding the metal sites show no channel to amino-terminal Ni^II and narrow lipophilic (hydrophobic) channel to carboxy-terminal Ni^II. Ni^II becomes trapped in the folded protein in a near octahedral geometry (yellow bonds; Supplementary Fig. 6) analogous to cognate Mn^II. The MncA model illustrates kinetic trapping of non-cognate metals suggesting MncA may be used to faithfully report in-cell metalation. Supplementary Fig. 7 shows that post-folding Ni^II did not exchange with Cu^II in vitro.