Expression and Activity of the BioH Esterase of Biotin Synthesis is Independent of Genome Context

BioH is a α/β‐hydrolase required for synthesis of the pimelate moiety of biotin in diverse bacteria. Among these bacteria the bioH gene is found in different genomic contexts. In some cases such as Escherichia coli the gene is not located within a biotin synthetic operon and its transcription is not coregulated with the other biotin synthesis genes. In other cases such as Pseudomonas aeruginosa the bioH gene is found within a biotin synthesis operon. Where it is is located immediately upstream of bioC , which encodes the methyltransferase that inserts the carboxyl methyl group eventually removed by the esterase activity of BioH. In such cases transcription of bioH is coregulated with the other biotin operon genes. Moreover, in these operons the bioH coding sequence often overlaps with those of the upstream and downstream genes consistent with translational coupling. The esterases of pimelate moiety synthesis show remarkable genomic plasticity in that in some biotin operons bioH is replaced by other α/β hydrolases of diverse sequence. The “wild card” nature of these enzymes led us to compare the paradigm “freestanding” E. coli BioH with the P. aeruginosa BioH encoded in a biotin synthetic operon. Our hypothesis was that the BioH encoded by an operon‐encoded gene might differ in its expression level and/or activity from the freestanding BioH gene. We report that this is not the case. The two BioH proteins show remarkably similar hydrolase activities and specificies, although Pseudomonas aeruginosa BioH is expressed at significantly higher levels than E. coli BioH. Despite the enzymatic similarities of the two BioH proteins, bioinformatics analysis places the freestanding and operon‐encoded BioH proteins into distinct clades. Support or Funding Information NIHThe E. coli biotin biosynthesis pathway and genetic organizations of the E. coli and P. aeruginosa biotin synthesis genes. (A), Scheme of the biotin synthesis pathway. (B) The biotin synthesis gene organizations of E. coli and P. aeruginosa . Note that in E. coli , the five bioABFCD genes are located within the biotin synthesis ( bio ) operon at min 17 of the chromosome map whereas the bioH gene is at min 74 of the genetic map and thus is well removed from the bio operon.