HYBRID PROTEINS OF THE TRANSGLYCOSYLASE AND THE TRANSPEPTIDASE DOMAINS OF PBP1B AND PBP3 OF ESCHERICHIA-COLI

The construction of hybrid proteins of PBP1B and PBP3 has been describ ed. One hybrid protein (PBP1B/3) contained the transglycosylase domain of PBP1B and the transpeptidase domain of PBP3. In the other hybrid p rotein, the putative transglgcosylase domain of PBP3 was coupled to th e transpeptidase domain of PBP1B (PBP3/1B). The hybrid proteins were l ocalized in the cell envelope in a similar way as the wild-type PBP1B. In vitro isolates of the strains containing the hybrid proteins had a transglycosylase activity intermediate between that of wild-type PBP1 B-producing strain and that of a PBP1B overproducer. Analysis with spe cific antibiotics against PBP1A/1B and PBP3 and mutant analysis in str ains containing PBP3/1B revealed no detectable effects in vivo compare d with wild-type strains. The same was show,vn for PBP1B/3 when the ex periments were performed in a recA background. The data indicate that the hybrid proteins cannot replace native penicillin-binding proteins. This finding suggests that functional high-molecular-weight penicilli n-binding protein specificity is at least in part determined by the un ique combination of the two functional domains.