Study “Wild” vs “Domesticated” BioH Proteins

Biotin is an essential vitamin required in all three domains of life. It consists of two fused rings and a valeric acid side‐chain ( Fig. 1). Despite the essential functions of biotin, de novo synthesis of this vitamin is restricted to bacteria, a few fungi, and plants. Humans cannot synthesize biotin as part of their normal metabolism and therefore rely on exogenous biotin supply. Thus, inhibition of the biotin synthesis pathway key enzymes is an attractive approach for antibiotic, fungicide, and herbicide development. Although the biotin synthesis pathway has been well demonstrated in bacteria, especially Escherichia coli, there is still a long standing puzzle that haven't been resolved yet. In E. coli , the biotin synthetic genes bioABCDF are clustered together at min 17 of the genetic map. However, the bioH gene is far removed from the other genes of the biotin synthetic pathway and is not regulated by the biotin synthetic repressor, BirA. Interestingly, in many proteobacteria (e.g., the pseudomonads), bioH is apparently located inside the biotin synthetic gene operon. Moreover, studies have shown that E. coli BioH is a rather promiscuous hydrolase. It not only cleaves the methyl group of pimeloyl‐ACP methyl ester as it functions in the biotin synthetic pathway, but also cleaves the ethyl, propyl and butyl esters of pimeloyl‐ACP and adipoyl‐ACP methyl ester. Another fascinating part is that BioH function seems like a “wild card” among the biotin synthetic enzymes since in some bacteria the bioH gene is displaced by other genes with the same function of BioH. Hence, it is reasonable to think that the E. coli BioH may be less specific and more active than those encoded by the more “domesticated” bioH genes found inside the biotin synthetic operon. Surprisingly, our current in vitro data showed that BioH from E. coli and P. aeruginosa have equal activity and similar substrate pools. On the other hand, the in vivo qRT‐PCR data showed that the expression level of the two of bioH genes do have some difference. We found that the expression level bioH gene in E. coli is less than that in P. aeruginosa. Support or Funding Information NIH