The Gene CBO0515 from Clostridium botulinum Strain Hall A Encodes the Rare Enzyme N ⁵ -(Carboxyethyl) Ornithine Synthase, EC 1.5.1.24

Abstract

Sequencing of the genome of Clostridium botulinum strain Hall A revealed a gene (CBO0515), whose putative amino acid sequence was suggestive of the rare enzyme N 5 -(1-carboxyethyl) ornithine synthase. To test this hypothesis, CBO0515 has been cloned, and the encoded polypeptide was purified and characterized. This unusual gene appears to be confined to proteolytic strains assigned to group 1 of C. botulinum.In the late 1980s, high concentrations of two unknown ninhydrin-reactive compounds were discovered in the amino acid pool of Lactococcus lactis, an organism used extensively for the manufacture of cheese in the dairy industry. The two compounds, subsequently identified as, were purified and characterized, and their stereochemical structures were established by chemical syntheses and nuclear magnetic resonance spectroscopy (11,14,17). These N-carboxyalkyl derivatives are formed enzymatically via a reductive condensation between pyruvic acid and the (side chain) amino groups of ornithine and lysine, respectively (Fig. 1).In L. lactis, the biosyntheses of N 5 -(CE) ornithine and N 6 -(CE) lysine are catalyzed by a unique tetrameric NADPHdependent enzyme, N 5