S100A15 binds zinc with distorted tetrahedral geometry. A. Sequence alignment of S100A15 (NP_789793.1), S100A7 (CAG46961.1), S100A12 (NP_005612.1) and S100B (CAG46920.1). Divergent residues between S100A15 and S100A7 are denoted as yellow triangles (zinc binding cluster) and green diamonds (predicted receptor binding cluster). B. Surface representation of S100A15 with one monomer shown in sky blue and the other in orange. Black arrow in the right panel denotes the flexibility of the surface loop to which the His90 zinc ligand is attached. C. Left panel – Fo-Fc electron density of the zinc binding site of S100A15 calculated at 1.5 sigma with zinc shown as a grey sphere and the chloride ligand shown as a yellow sphere. Right panel – Anomalous difference electron density map of S100A7D24G using data collected at the zinc edge of 1.2482 nm calculated at 5 sigma confirming that the bound metal is zinc. All figures were generated with PyMol.