Search

In Streptomyces davawensis roseoflavin is synthesized from GTP and ribulose-5-phosphate through riboflavin. As a first step towards the molecular analysis of flavin metabolism in S. davawensis the genes involved in riboflavin biosynthesis were cloned by hybridization of heterologous probes to a genomic library on a high-density colony-array. The genes ribB (riboflavin synthase, α-chain; EC 2.5.1.9), ribM (putative membrane protein), ribA (bifunctional GTP cyclohydrolase II/3,4-dihydroxy-2-butanone-4-phosphate synthase; EC 3.5.4.25) and ribH (lumazine synthase; EC 2.5.1.9) are organized in an operon-like cluster. Northern blot analysis of this cluster revealed two transcripts of 1.7 and 3.1 kb, respectively. The gene ribB was overexpressed in Escherichia coli. The specific riboflavin synthase activity in a cell-free extract of a recombinant strain was 0.246 nmol mg−1 min−1. Overexpression of ribM enhanced the transport of riboflavin in the corresponding recombinant E. coli strain. Furthermore, overexpression of ribM increased roseoflavin sensitivity of E. coli. On another subgenomic fragment a putative S. davawensis ribG gene coding for the missing pyrimidine deaminase/reductase (EC 3.5.4.26 and EC 1.1.1.193) of the riboflavin biosynthetic pathway and ribY coding for a second (monofunctional) GTP cyclohydrolase II were identified. [ABSTRACT FROM AUTHOR]

Flavins are active components of many enzymes. In most cases, riboflavin (vitamin B2) as a coenzyme represents the catalytic part of the holoenzyme. Riboflavin is an amphiphatic molecule and allows a large variety of different interactions with the enzyme itself and also with the substrate. A great number of active riboflavin analogs can readily be synthesized by chemical methods and, thus, a large number of possible inhibitors for many different enzyme targets is conceivable. As mammalian and especially human biochemistry depends on flavins as well, the target of the inhibiting flavin analog has to be carefully selected to avoid unwanted effects. In addition to flavoproteins, enzymes, which are involved in the biosynthesis of flavins, are possible targets for anti-infectives. Only a few flavin analogs or inhibitors of flavin biosynthesis have been subjected to detailed studies to evaluate their biological activity. Nevertheless, flavin analogs certainly have the potential to serve as basic structures for the development of novel anti-infectives and it is possible that, in the future, the urgent need for new molecules to fight multiresistant microorganisms will be met. [ABSTRACT FROM AUTHOR]