Fig. 7: The stanniocalcin-2 (STC2) dimer is suspended centrally in the PAPP-A·STC2 structure.
a Cartoon representation in two orientations of the PAPP-A·STC2 complex with the M domains (cyan), the SCR domains (blue), the C domain (light blue) including LNR3 (green), and the STC2 dimer (gray/pink) shown to emphasize the position of the STC2 dimer within the complex. This color scheme is used throughout the figure. b Cartoon representation of the STC2 dimer (R44-C211) of the PAPP-A·STC2 complex in different orientations, as indicated, to emphasize the relative orientation of the α-helices. Disulfide bonds are indicated. The density map around the C211-C211 dimerization disulfide bond is shown (right panel, position in the structure is indicated with a rectangle on the left panel). The map (composite map) was contoured at 7 σ. c The interface between STC2 and the PAPP-A C domain. Basic residues of STC2 positioned favorably for electrostatic interaction with the negative charge surrounding the Ca2+ ion of LNR3 are indicated. Residues likely to be involved in van der Waal interactions are also indicated (V63 of STC2; Y1566, T1594, and K1592 of PAPP-A). Note that STC2 residues interact with the C domain of the PAPP-A subunit to which the opposite STC2 subunit is disulfide bound.
