The gac-gene cluster for the production of acarbose from Streptomyces glaucescens GLA.O—Identification, isolation and characterization

The C7N-cyclitol containing α-glucosidase inhibitor acarbose is commercially produced using developed strains of Actinoplanes and is used in the treatment of patients suffering from diabetes type II. We have identified a second acarbose production cluster using a genomic cosmid gene bank from Streptomyces glaucescens GLA.O and sequenced a region (42658 bp; accession AM409314) which clearly contained a gene cluster (gac-cluster) for the synthesis of acarbose or acarbose related endproducts. The gac-cluster exhibited large similarities to the acb-gene cluster from Actinoplanes. However, remarkable differences are found in the biosynthesis of the C7N-cyclitol in the two acarbose biosynthesis pathways. We show the expression of selected genes using RT-PCR approaches, we were able to detect small amounts of acarbose or acarbose related metabolites and we have characterized the GacK protein, an acarbose kinase, which specifically phosphorylates acarbose and acarbose homologs. All these data in combination with the postulated functions of the encoded Gac proteins clearly indicate that also in S. glaucescens a recycling mechanism for acarbose (“carbophor”) which had been described for the first time for acarbose cluster from Actinoplanes, is also realised.