Fig. 3.

Crystal structures of hSPSB1, SPSB2, and SPSB4. (a) Overview of the structures of hSPSB1 in complex with hPar-4 and VASA, as well as the hSPSB2 complex with VASA and apo-hSPSB4. Peptide ligands are shown as sticks. (b) Molecular surface representation of hSPSB structures. The electrostatic surface potential is conserved across the hPar-4 binding site, but more varied beyond this epitope. (c) Sequence alignment of SPRY domain structures in the SPSB family. Secondary-structure elements are shown for hSPSB1, including binding loops A–E. Key hPar-4 contact residues are indicated by asterisks. Red and yellow shading indicate positions with sequence identity and sequence similarity, respectively. An enhanced 3D visualization file displaying all structures is available for download (file S6).