FIGURE 4.

Molecular modeling of the TEM-1 β-lactamase acyl-intermediate. A, the acyl-intermediate with TEM-1 (in green) covalently bonded to penicillin G is shown to illustrate that the benzene ring of penicillin (in yellow) is close to Asn¹⁷⁰ (Protein Data Bank code 1FQG) (20). The carbon position that contains the amine group in ampicillin is 3.2 Å away from the side chain of Asn¹⁷⁰. B, when ampicillin and the glycine 170 substitution are modeled into the acyl-intermediate structure, the alpha carbon of glycine is 4.5 and 6.0 Å from the primary amine and the benzene ring of the ampicillin R substituent, respectively. C, TEM-1 ampicillin acyl-enzyme model from B with the alanine substitution modeled into position 170.