AmpC and AmpH, proteins related to the class C beta-lactamases, bind penicillin and contribute to the normal morphology of Escherichia coli

Abstract

Two proteins that bind penicillin were observed in Escherichia coli infected with phages 141, 142, 650, and 651 from the Kohara genomic library. These phages carry chromosomal DNA fragments that do not contain any known penicillin binding protein (PBP) genes, indicating that unrecognized gene products were exhibiting penicillin binding activity. The genes encoding these proteins were subcloned, sequenced, and identified. One gene was ampC, which encodes a chromosomal class C ␤-lactamase. The second gene was located at about 8.5 min on the E. coli genomic map and is a previously uncharacterized open reading frame, here named ampH, that encodes a protein closely related to the class C ␤-lactamases. The predicted AmpH protein is similar in length to AmpC, but there are extensive alterations in the amino acid sequence between the SXXK and YXN motifs of the two proteins. AmpH bound strongly to penicillin G, cefoxitin, and cephalosporin C; was temperature sensitive; and disappeared from cells after overnight incubation in stationary phase. Although closely related to AmpC and other class C ␤-lactamases, AmpH showed no ␤-lactamase activity toward the substrate nitrocefin. Mutation of the ampC and/or ampH genes in E. coli lacking PBPs 1a and 5 produced morphologically aberrant cells, particularly in cell filaments induced by aztreonam. Thus, these two members of the ␤-lactamase family exhibit characteristics similar to those of the classical PBPs, and their absence affects cell morphology. These traits suggest that AmpC and AmpH may play roles in the normal course of peptidoglycan synthesis, remodeling, or recycling.

Biochemistry and Comparative Genomics of SxxK Superfamily Acyltransferases Offer a Clue to the Mycobacterial Paradox: Presence of Penicillin-Susceptible Target Proteins versus Lack of Efficiency of Penicillin as Therapeutic Agent

“…coli produces two additional chromosome-encoded freestanding SxxK acyltransferases, AmpC and AmpH (99). They are similar in sequence.…”

Peptidoglycan Hydrolases of Escherichia coli

“…The five high-molecular-mass (HMM) PBPs (PBP1a, PBP1b, PBP1c, PBP2, and PBP3) catalyze the extracytoplasmic reactions of PG polymerization and are devoid of hydrolytic activity (76,229). Among the eight low-molecular-mass (LMM) PBPs (PBP4, PBP4b, PBP5, PBP6, PBP6b, PBP7/8, AmpC, and AmpH), only the ␤-lactamase AmpC has no recognized DD-peptidase activity (95). The E. coli LMM PBPs belong to four subcategories of the class C subdivision of the PBP classification (229): type 4 (PBP4), type 5 (PBP5, PBP6, and PBP6b), type 7 (PBP7/8), and type AmpH (PBP4b and AmpH).…”

“…E. coli PBPs are visualized by polyacrylamide gel electrophoresis after the treatment of cells with radiolabeled or fluorescence-labeled ␤-lac- tams and are designated according to their electrophoretic migrations (6,49,72,95,103,186,243,291,315). Most PBPs are anchored to the cytoplasmic membrane with their active site in the periplasm (73).…”

FtsK is an essential cell division protein that is localized to the septum and induced as part of the SOS response

“…CS12-7 (dacA) and its isogenic parent CS109 were obtained from K. Young (Henderson et al, 1997). DM511 [lexA (Ts)] was obtained from D. Mount (Mount et al, 1973).…”