Extended Data Fig. 5: Bcs3 protomer dimerization contacts.

a-c, Contacts and ribbon representations are colored as follows: CroT (orange), CrpP (yellow), CriT (red), and SH3b domain (tan). In panel b, the dimer from the Bcs3-CMP complex is shown in two representations. Top: The protomer containing the CroT-CMP complex is shown in ribbons and the complementary protomer in a surface representation (up to the dashed line). Bottom: The protomer containing the CroT-CMP complex is shown in a surface representation and the complementary protomer is shown in ribbons (below the dashed line). The panels a and c present 90° rotations of the individual protomers in surface representation, disclosing the surface contacts between protomers by coloring contacting residues according to the enzyme they belong to. Note the conservation of the main interactions in the center of the protomers that correspond to interactions between CrpP and CriT’, and CrpP’ and CriT. The HB-1 of CriT mediates the interaction of CriT with the phosphatase CrpP and the SH3b domain of the same protomer, as well as with the ribose transferase CriT’ of the other protomer (see HB-1 in Fig. 2a-c). The HB-2 mediates the interaction of CriT with (i) CrpP’ and (ii) the C-terminal Rossmann-fold domain of CroT’ from the neighboring protomer. In contrast, HB-3 is mainly exposed to the solvent. Two encircled regions in the protomers, 1 and 1’ for CriT and CriT’ (a, c), and 2 and 2’ for CroT and CroT’ (a, c), display variability associated with the conformational changes in the CriT-CroT’ and CriT’-CroT interphase. These changes in the interaction correlate with the presence or absence of CMP in CroT. The contacts visualized above are mediated by the following structural elements (secondary structural elements are shown in Supplementary Data 1): (i) the α42 (residues 756–761) of CriT interacts with α11 (residues 207–210) and α14 (residues 240–248) of CroT, and (ii) α43 (residues 770–780) of CriT interacts with α11 (residues 207–210), the loop connecting β7-α11 (residues 196–206), and α17 (residues 300–303) of CroT. Furthermore, (i) α24 (residues 419–423) of CrpP interacts with the α34-α35 loop (residues 607–612), the α47-α48 loop (residues 923–928), and α48 (residues 929–946) of CriT, (ii) the long α25 (residues 425–443) of CrpP interacts with α39 (residues 722–725), the α39-α40 loop (residues 726–736), β22-α45 loop (residues 818–823), β23-β24 loop (residues 848–857), β24-α46 loop (863–869), and α48 (929–946) of CriT, (iii) the α26-α27 loop (residues 468–470) of CrpP interacts with the end of α36 (residues 638–669) of CriT, and (iv) α26 (residues 456–467) of CrpP interacts with the end of α36 (residues 638–669), β24 (858–862), β23-β24 loop (residues 848–857), and β24-α46 loop (863–869) of CriT.