Betaine aldehyde dehydrogenase from Pseudomonas aeruginosa: cloning, over-expression in Escherichia coli, and regulation by choline and salt
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In the human pathogen Pseudomonas aeruginosa, betaine aldehyde dehydrogenase (BADH) may play a dual role assimilating carbon and nitrogen from choline or choline precursors—abundant at infection sites—and producing glycine betaine, which protects the bacteria against the high-osmolarity stress prevalent in the infected tissues. We cloned the P. aeruginosa BADH gene and expressed the BADH protein in Escherichia coli. The recombinant protein appears identical to its native counterpart, as judged by Western blot, N-terminal amino acid sequence, tryptophan-fluorescence emission spectra, circular-dichroism spectroscopy, size-exclusion chromatography, and kinetic properties. Computational analysis indicated that the promoter sequence of the putative operon that includes the BADH gene has a consensus-binding site for the choline-sensing transcription repressor BetI, and putative boxes for ArcA and Lrp transcription factors but no known elements of response to osmotic stress. This is consistent with the strong induction of BADH expression by choline and with the lack of effect of NaCl. As there were significant amounts of BADH protein and activity in P. aeruginosa cells grown on glucose plus choline, as well as the BADH activity exhibiting tolerance to salt, it is likely that glycine betaine is synthesized in vivo and could play an important osmoprotectant role under conditions of infection.
KeywordsPseudomonas aeruginosa Betaine aldehyde dehydrogenase Bet system Computational promoter analysis Choline induction Salt inhibition
We thank Dr. G. Mendoza, Faculty of Medicine, UNAM, for N-terminal sequencing the recombinant protein, and the laboratory of Fisicoquímica e Ingeniería de Proteínas, Faculty of Medicine, UNAM, for giving us access to the CD equipment. This work was supported by grants to RAM-C from Consejo Nacional de Ciencia y Tecnología (CONACYT 2552P-N and 37820-N).
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