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Figure 4
X-ray structural analysis of different MIII·DTPA-NH2 chelate complexes bound to the Anticalin CL31d. (a) Superposition of the different CL31d structures with bound DTPA-NH2 chelate complexes of Bi3+ (cyan C atoms), Tb3+ (green), Dy3+ (orange), Lu3+ (yellow), Sc3+ (salmon) and the previously published Y3+·DTPA-SCN complex (white; PDB entry 4iax), as well as the metal-free DTPA-NH2 (purple; from co-crystallization with Ga3+) using a set of 58 structurally conserved Cα atoms of the lipocalin scaffold. (b) Individual MIII·DTPA-NH2 complexes from the co-crystal structures with the Anticalin CL31d or CL31 together with the metal-coordinating water molecule (dashed lines indicate the eightfold or ninefold metal coordination). (c) Exemplary 2Fo − Fc electron densities for the DTPA-NH2 complexes of Sc3+ (left) and Bi3+ (center) in comparison with the metal-free chelate ligand (obtained in the presence of Ga3+), which harbors a water molecule at the position of the central ion (right). The 2Fo − Fc electron densities are contoured at 1σ in blue for DTPA-NH2 and additonally at 3σ in yellow-orange for the central ion or water molecule.

Journal logoSTRUCTURAL BIOLOGY
COMMUNICATIONS
ISSN: 2053-230X
Volume 82| Part 9| September 2026| Pages 301-311
https://doi.org/10.1107/S2053230X26007624