Regulation of Geldanamycin Biosynthesis by Cluster-Situated Transcription Factors and the Master Regulator PhoP.

Geldanamycin and the closely related herbimycins A, B, and C are benzoquinone-type ansamycins with antitumoral activity. They are produced by var. , and among other strains. Geldanamycins interact with the Hsp-90 chaperone, a protein that has a key role in tumorigenesis of human cells. Geldanamycin is a polyketide antibiotic and the polyketide synthase contain seven modules organized in three geldanamycin synthases genes named , , and . The loading domain of GdmI activates AHBA, and also related hydroxybenzoic acid derivatives, forming geldanamycin analogues. Three regulatory genes, , , and were found associated with the geldanamycin gene cluster in strains. GdmRI and GdmRII are LAL-type (large ATP binding regulators of the LuxR family) transcriptional regulators, while GdmRIII belongs to the TetR-family. All three are positive regulators of geldanamycin biosynthesis and are strictly required for expression of the geldanamycin polyketide synthases. In the regulates geldanamycin biosynthesis and also expression of genes in the elaiophylin gene cluster, an unrelated macrodiolide antibiotic. The biosynthesis of geldanamycin is very sensitive to the inorganic phosphate concentration in the medium. This regulation is exerted through the two components system PhoR-PhoP. The genes of are linked to encoding a transcriptional modulator. The gene was deleted in var and the mutant was unable to grow in SPG medium unless supplemented with 5 mM phosphate. Also, the gene involved in the high affinity phosphate transport was cloned, and PhoP binding sequences (PHO boxes), were found upstream of , , and ; sequences were confirmed by EMSA and nuclease footprinting protection assays. The PhoP binding sequence consists of 11 nucleotide direct repeat units that are similar to those found in and other species. The available genetic information provides interesting tools for modification of the biosynthetic and regulatory mechanisms in order to increase geldanamycin production and to obtain new geldanamycin analogues with better antitumor properties.