IDENTIFICATION AND ANALYSIS OF A GENE ENCODING L-2,4-DIAMINOBUTYRATE-2-KETOGLUTARATE 4-AMINOTRANSFERASE INVOLVED IN THE 1,3-DIAMINOPROPANE PRODUCTION PATHWAY IN ACINETOBACTER-BAUMANNII

The ca. 2.2-kbp region upstream of the ddc gene encoding L-2,4-diamino butyrate decarboxylase in Acinetobacter baumannii was sequenced and fo und to contain another open reading frame of 1,338 nucleotides encodin g a protein with a deduced molecular mass of 47.323 Da. Analysis of th e homologies observed from the deduced amino acid sequence indicated t hat the gene product is an enzyme belonging to subgroup II of the amin otransferases. This was first verified when examination of the crude e xtracts from Escherichia coli transformants led to detection of a nove l aminotransferase activity catalyzing the following reversible reacti ons: L-2,4-diaminobutyric acid + 7-ketoglutaric acid<->L-glutamic acid + L-aspartic beta-semialdehyde. Further confirmation was obtained whe n the gene was overexpressed in E. coli and the corresponding protein was purified to homogeneity. It catalyzed the same reactions and its N -terminal amino acid sequence was consistent with that deduced from th e nucleotide sequence, Therefore, the gene and its product were named dar and L-2,4-diaminobutyrate:2-ketoglutarate 4-aminotransferase (DABA AT), respectively, Feeding experiments of A. baumannii with L-[U-C-14 ]aspartic acid resulted in the incorporation of the label into 1,3-dia minopropane Apparent homologs of dat and DABA AT were detected in othe r Acinetobacter species by PCR amplification and Western blotting, The se results indicate that the dat gene (as well as the dde gene) partic ipates in the synthesis of 1,3-diaminopropane, the only diamine found in this genus. However, the biological role, if one exists, of 1.3-dia minopropane synthesis is unknown.