Fig. 4: Structural properties of the binding interfaces between PAPP-A and proMBP or STC2.
From: Structural insights into the covalent regulation of PAPP-A activity by proMBP and STC2
a The representation of the four interfaces between PAPP-A and proMBP with PAPP-A shown in color-coded surface and proMBP in the cartoon. The boxes represent the close-up details shown in b–e. b The interface between proMBP and SD. Cys169 of proMBP and Cys652 of SD that form a disulfide bond are shown as ball-and-stick. The indole of Trp191 insets into a hydrophobic groove of the SD. Arg170 and Phe172 of proMBP form two hydrogen bonds with Val691 and His689 of SD, respectively (red dashed lines). c The interface between proMBP and CTD. Arg214–Phe1481 and Arg208–Tyr1486 form two cationic–π stacks (black dashed lines) and Ala187–Lys1512 form a hydrogen bond. d The interface between proMBP and LNR1–2. Side chains of His137 and Asn138 from proMBP and Arg338, Asn343, and Phe368 from LNR1–2 form several hydrogen bonds and hydrophobic stacks. e The interface between proMBP and βBD. Two perpendicular helices form several pairs of interactions that include Tyr143 of proMBP, Gln998 of βBD, Ser150 of proMBP, and Tyr996 of βBD. f Structural representation of the interactions between PAPP-A and STC2 (same view as in a). The close-up views are presented in g and h. g The interface between STC2 and SD (same view as in b). Cys120 of STC2 and Cys652 of PAPP-A form a disulfide bond. Two other hydrogen bonds are formed by Arg123 and His55 from STC2 and His689 and Asp726 from SD, respectively. h The interface between STC2 and CTD (same view as in c). The side chain of Lys104 from STC2 inserts into a groove formed by Phe1481, Tyr1486, and Phe1516, creating a strong interaction. The main chain of Met1518 of PAPP-A and Leu89 of STC2 form a hydrogen bond.
