Characterization of a Bordetella pertussis diaminopimelate (DAP) biosynthesis locus identifies dapC, a novel gene coding for an N-Succinyl-L,L-DAP aminotransferase

The functional complementation of two Escherichia coli strains defective in the succinylase pathway of meso-diaminopimelate (meso DAP) biosynthesis wi th a Bordetella pertussis gene library resulted in the isolation of a putat ive dap operon containing three open reading frames (ORFs), In line with th e successful complementation of the E, coli dapD and dapE mutants, the dedu ced amino acid sequences of two ORFs revealed significant sequence similari ties with the DapD and DapE proteins of E, coli and many other bacteria whi ch exhibit tetrahydrodipicolinate succinylase and N-succinyl-L,L-DAP desucc inylase activity, respectively, The first ORF within the operon showed sign ificant sequence similarities with transaminases and contains the character istic pyridoxal-5'-phosphate binding motif, Enzymatic studies revealed that this ORF encodes a protein with N-succinyl-L,L-DAP aminotransferase activi ty converting N-succinyl-2-amino-6-ketopimelate, the product of the succiny lase DapD, to N-succinyl-L,L-DAP, the substrate of the desuccinylase DapE, Therefore, this gene appears to encode the DapC protein of B, pertussis, Ap art from the pyridoxal-5'-phosphate binding motif, the DapC protein does no t show further amino acid sequence similarities with the only other known e nzyme with N-succinyl-L,L-DAP aminotransferase activity, ArgD of E. coli.