Figure 4

The allosteric ligand-binding loop is important for HtrA oligomer stabilization. (A) Model of HtrA showing the domain structure showing the signal peptide (SP), the extended linker region containing the LA loop, the protease domain with the catalytic triad histidine (H), aspartic acid (D), and serine (S), and the PDZ1 and PDZ2 domains. The protease domain also contains the regulatory LD, L1, L2, and L3 loops. The position of the ligand-binding loop is highlighted in red. (B) X-ray structure of the protease domain of HpHtrA⁴⁶ with S₁₆₄, D₁₆₅, S₁₆₆, and D₁₆₈ indicated in the ligand-binding loop. S₂₂₁ in the active center is highlighted in magenta. (C) Oligomerization and activity of HpHtrA wt, HpHtrA S₁₆₄A, HpHtrA D₁₆₅A, HpHtrA S₁₆₆A, HpHtrA D₁₆₈A, and HpHtrA S₂₂₁A analyzed by casein zymography (lanes 1–6), non-reducing SDS-PAGE (lanes 7–12), and reducing SDS-PAGE (lanes 13–18).