Modeling the bacterial AcpS–ACP complex. (a) Stereogram of the least-squares superposition of the AcpSSA (red), AcpSBA (green) and AcpSBS–ACPBS (AcpS, black; ACP, light blue ribbon) structures. Two 3′,5′-ADP molecules in the B. anthracis structure are shown a sticks. (b) Stereo close-up view of (a) showing ADPII in the AcpSBA structure clashing with the α3 helix of ACPBS. Asp35, PN2-36 (P-pant-modified Ser36) and Leu37 of ACP are depicted as lines and colored by element: C, blue; O, red; N, dark blue; P, orange.