Expression of the second lysine decarboxylase gene of Escherichia coli

Abstract

Certain amino acids are substrates for two decarboxylase enzymes in Escherichia coli, one inducible by anaerobic growth a t low pH and the other constitutive. In the case of lysine, an inducible decarboxylase (CadA) has been extensively characterized, but evidence for the existence of a second lysine decarboxylase is fragmentary and uncertain. This paper confirms that a second lysine decarboxylase is encoded by a locus (Idc) previously suggested to be a lysine decarboxylase gene on the basis of sequence comparisons. Overexpression of the cloned gene provided sufficient quantities of enzyme in cell-free extracts for preliminary examination of the properties of the Idc gene product, Ldc. The enzyme is active over a broad range of pH with an optimum a t 7.6, much higher than that of CadA, about 55. The temperature optimum for both enzymes is similar, a t about 52 "C, but Ldc is more readily inactivated by heat than CadA. Expression of Idc from its own promoter was very weak for cells growing in a variety of media, although a low level of lysine decarboxylase was present in cells that carried the Idc region on an oligo-copy plasmid when these were grown in minimal-glucose medium. Northern analysis of RNA extracted from such cells revealed a transcript whose length corresponded to that of the Idc gene, suggesting that Idc is normally transcribed from a promoter immediately upstream. However, most of the Idc mRNA was shorter, indicating degradation or premature termination. The Idc upstream sequence promoted transcription of a lac2 gene to which it was fused. Introduction of the upstream sequence as an insert in a multicopy vector increased transcription of the resident lac2 fusion. The low level of expression in single copy, the emergence of expression when the gene is present at moderate copy number, and the derepression by the upstream sequence in trans imply that this second lysine decarboxylase gene may not be constitutive but subject to specific repression by a factor which remains to be identified.

Regulation of Vibrio cholerae Genes Required for Acid Tolerance by a Member of the “ToxR-Like” Family of Transcriptional Regulators

“…E. coli is known to possess both biosynthetic and biodegradative lysine decarboxylases, Lcd and CadA, respectively. Lcd is responsible for the constitutive, low-level biosynthesis of cadaverine from lysine (17,19). However, after acid induction, the bulk of lysine decarboxylase activity is due to the induction of cadA (23,29).…”

Formation of a Distinctive Complex between the Inducible Bacterial Lysine Decarboxylase and a Novel AAA+ ATPase

“…6B, panel 5). However, the enzymatic activity profile and stability of LdcC differ from that of LdcI (63,64). Due to the high sequence similarity between LdcC and LdcI, we expected that LdcC might also bind RavA, however, we were surprised to find that there is no significant interaction between RavA and LdcC (Fig.…”

“…LdcI and LdcC are 69% identical and 84% similar as determined using pairwise BLAST P analysis. LdcC is expressed in E. coli at very low levels, and its exact role in the cell remains unclear (63,64). Like LdcI, LdcC is also a PLP-dependent enzyme that decarboxylates lysine and possibly assembles into a decamer (63,64) (Fig.…”

Centromere Binding and Evolution of Chromosomal Partition Systems in the Burkholderiales

“…Directed mutagenesis of the putative HTH of B. cenocepacia J2315 c3 and Ralstonia pickettii 12D plasmid 1parB genes in pDAG127 was ordered from GenScript. Recombinant plasmids, verified by sequencing, were electroporated into the Escherichia coli strain DLT812 (36). Cells grown in LB medium at 37°C to an optical density at 600 nm (OD 600 ) of 0.25 were induced with 0.1% arabinose (final concentration), incubated for 4 h at 37°C, and chilled on ice for 10 min.…”