The glucokinases from Streptomyces peucetius var. caesius

Glucokinases (Glks) are enzymes of the glycolytic pathway involved in glucose phosphorylation. These enzymes can use various phosphoryl donors such as ATP, ADP, and polyphosphate. In several streptomycetes, the ATP-dependent Glk (ATP-Glk) has been widely studied and regarded as the main glucose phosphorylating enzyme and also is likely a regulatory protein involved in carbon catabolite repression. In cell-extracts from the doxorubicin overproducing strain Streptomyces peucetius var. caesius, grown in glucose, a polyphosphate-dependent Glk (Pp-Glk) was detected by zymogram. Contrary to wild type strains of Streptomyces coelicolor, Streptomyces lividans and Streptomyces thermocarboxydus K-155, S. peucetius var. caesius, produced 1.8 times more Pp-Glk than ATP-Glk. In addition, this microorganism produced 5 and 4- times more Pp-Glk and anthracyclines, respectively than its wild type Streptomyces peucetius parent strain, supporting a role for this enzyme in antibiotic production in the overproducer strain. A cloned 726 bp DNA fragment from S. peucetius var. caesius encoded a putative Pp-Glk, with amino acid identities between 83-87% to orthologous sequences from the above cited streptomycetes. The cloned fragment showed the putative polyphosphate binding sequences GXDIGGXXIK, TXGTGIGSA and KEX₍₄₎SWXXWA. Sequences for the Zn-binding motif were not detected in this fragment, suggesting that Pp-Glk is not related to the Glk ROK family of proteins.