Characterization and sequence of Escherichia coli pabC, the gene encoding aminodeoxychorismate lyase, a pyridoxal phosphate-containing enzyme

Abstract

In Escherichia coli, p-aminobenzoate (PABA) is synthesized from chorismate and glutamine in two steps. Aminodeoxychorismate synthase components I and II, encoded by pabB and pabA, respectively, convert chorismate and glutamine to 4-amino-4-deoxychorismate (ADC) and glutamate, respectively. ADC lyase, encoded by pabC, converts ADC to PABA and pyruvate. We reported that pabC had been cloned and mapped to 25 min on the E. coli chromosome (J. M. Green and B. P. Nichols, J. Biol. Chem. 266:12971-12975, 1991). Here we report the nucleotide sequence of pabC, including a portion of a sequence of a downstream open reading frame that may be cotranscribed with pabC. A disruption of pabC was constructed and transferred to the chromosome, and the pabC mutant strain required PABA for growth. The deduced amino acid sequence of ADC lyase is similar to those of Bacillus subtilis PabC and a number of amino acid transaminases. Aminodeoxychorismate lyase purified from a strain harboring an overproducing plasmid was shown to contain pyridoxal phosphate as a cofactor. This finding explains the similarity to the transaminases, which also contain pyridoxal phosphate. Expression studies revealed the size of the pabC gene product to be approximately 30 kDa, in agreement with that predicted by the nucleotide sequence data and approximately half the native molecular mass, suggesting that the native enzyme is dimeric.