Conformational flexibility of the active-site lid in LdtMt2Δ130. (a, b) Three different views of the electrostatic potential surface diagrams of mercury-derivatized (a) and meropenem-complexed LdtMt2Δ130 (b). The closed conformation of the active-site lid in (b) reveals that meropem attached to catalytic Cys354 is accessible through three narrow paths (Paths A, B and C). (c) The active-site lids in meropenem-complexed (cyan) and mercury-derivatized (magenta) LdtMt2Δ130 are shown as ribbon models with the surface of the meropenem complex. Residues that show large shifts upon lid closure are shown as stick models; the movement is indicated by black dotted arrows. The two models are in the same orientation.