AMPC AND AMPH, PROTEINS RELATED TO THE CLASS-C BETA-LACTAMASES, BIND PENICILLIN AND CONTRIBUTE TO THE NORMAL MORPHOLOGY OF ESCHERICHIA-COLI

Two proteins that bind penicillin were observed in Escherichia coli in fected with lambda phages 141, 142, 650, and 651 from the Kohara genom ic library, These phages carry chromosomal DNA fragments that do not c ontain any known penicillin binding protein (PBP) genes, indicating th at unrecognized gene products were exhibiting penicillin binding activ ity, The genes encoding these proteins were subcloned, sequenced, and identified, One gene was ampC, which encodes a chromosomal class C bet a-lactamase. The second gene was located at about 8.5 min on the E. co li genomic map and is a previously uncharacterized open reading frame, here named ampH, that encodes a protein closely related to the class C beta-lactamases, The predicted AmpM protein is similar in length to AmpC, but there are extensive alterations in the amino acid sequence b etween the SXXK and YXN I motifs of the two proteins. AmpH bound stron gly to penicillin G, cefoxitin, and cephalosporin C; was temperature s ensitive; and disappeared from cells after overnight incubation in sta tionary phase. Although closely related to AmpC and other class C beta -lactamases, AmpH showed no beta-lactamase activity toward the substra te nitrocefin, Mutation of the ampC and/or ampH genes in E. coli lacki ng PBPs 1a and 5 produced morphologically aberrant cells, particularly in cell filaments induced by aztreonam, Thus, these two members of th e beta-lactamase family exhibit characteristics similar to those of th e classical PBPs, and their absence affects cell morphology. These tra its suggest that AmpC and AmpH may play roles in the normal course of peptidoglycan synthesis, remodeling, or recycling.