Figure 4

Side view of FabZ active tunnel B surface with fatty acids of different lengths modeled to ACP. The electrostatic surface and ribbons were generated by Pymol. The color range from red (negative) to blue (positive) represents the surface electrostatic potentials of −75 e/kT to +75 e/kT. ACP is colored in magenta. Fatty acid chains with 4, 6, 8, 10, 12, 14 and 16 carbons are colored in hot pink, purple blue, yellow, salmon, gray, slate and orange, respectively. Secondary structural elements, tunnels I and II are labeled. (A) Side view of FabZ active tunnel B surface with fatty acids of different lengths modeled to ACP. Catalytic residues His58′ and Glu72, and residue Gly79 in the Y-shaped tunnel fork are shown as sticks. (B) Side view of FabZ active tunnel surface with short fatty acid chains (4-12 carbons). Short fatty acid chains and residues involved in the interactions are shown as sticks, and long chains with 14 and 16 carbons are shown as lines. The closed conformation of backdoor residue Phe83 (pointing toward Ile98) shown here is replaced by the corresponding residue from native HpFabZ structure (PDB code: 2GLL). It blocks long fatty chain (shown as a line) stretching to tunnel II. (C) Side view of FabZ active tunnel surface with long fatty acid chains (14 and 16 carbons). Long fatty acid chains and residues involved in the interactions are shown as sticks, and short chains are shown as lines. Phe83 adopts an open conformation (pointing to Ile93) and allows long fatty chains (shown as sticks) to stretch into tunnel II.