Gene cloning, purification, and characterization of 2,3-diaminopropionate ammonia-lyase from Escherichia coli

2,3-Diaminopropionate ammonia-lyase (DAPAL), which catalyzes alpha,beta-elimination of 2,3-diaminopropionate regardless of its stereochemistry, was purified from Salmonella typhimurium. We cloned the Escherichia coli ygeX gene encoding a putative DAPAL and purified the gene product to homogeneity. The protein obtained contained pyridoxal 5'-phosphate and was composed of two identical subunits with a calculated molecular weight of 43,327. It catalyzed the alpha,beta-elimination of both D- and L-2,3-diaminopropionate. The results confirmed that ygeX encoded DAPAL. The enzyme acted on D-serine, but its catalytic efficiency was only 0.5% that With D-2,3-diaminopropionate. The enzymologic properties of E. coli DAPAL resembled those of Salmonella DAPAL, except that L-serine, D- and L-beta-Cl-alanine were inert as substrates of the enzyme from E. coli. DAPAL had significant sequence similarity with the catalytic domain Of L-threonine dehydratase, which is a member of the fold-type II group of pyridoxal phosphate enzymes, together with D-serine dehydratase and mammalian serine racemase.