A remote surface loop modulates core structure and cold activity in phosphopantetheine adenylyltransferase
Fig 6
Comparison of structural and electrostatic basis in the MpaPPAT and MpaPPAT(Δ67–71) mutant.
(A) Superposition of the hexameric core structures of wild-type MpaPPAT (green) and the MpaPPAT(Δ67–71) mutant (cyan). The close-up view highlights the conformational changes at the trimer-trimer interface, particularly around α-helix H4. The deletion of the distal SCRLS loop induces a long-range effect that stabilizes the H4-associated loop in the mutant (involving residues D92 and D95), leading to a “clamped” and rigidified core. An ATP molecule (stick model) from the EcoPPAT structure (PDB code 1GN8) is superimposed to illustrate the proximity of the active site to the clamped interface. (B) Electrostatic surface potential comparison of the central pore (viewed along the 3-fold axis). The wild-type enzyme (left) features a wide, positively charged (blue) central channel, essential for the electrostatic steering of negatively charged substrates. Conversely, the mutant (right) displays a constricted, negatively charged (red) pore, creating an electrostatic barrier that repels substrates. Blue and red represent positive and negative potentials, respectively (±5 kT/e).