Identification of binding protein of virginiae butanolide C, an autoregulator in virginiamycin production, from Streptomyces virginiae.

In Streptomyces virginiae, production of virginiamycin is triggered by signal molecules named virginiae butanolide A, B or C (VB-A, B or C: Yamada, Y. et al. J. Antibiotics 40: 496-504, 1987). We have found a specific VB-C binding protein from S. virginiae, and characterized it by using a tritium-labeled VB-C analogue as a ligand. By equilibrium dialysis in the absence and presence of radio-inert VB-C, a crude extract from 1 g of wet mycelia specifically bound 3.5 pmol of [3H]VB. The binding disappeared after pronase digestion and showed ligand specificity toward cis VB-C (cis VB-C greater than trans VB-C much greater than A-factor type), indicating that binding was due to a cis VB-C specific binding protein. Scatchard analysis of the binding demonstrated a single class of high affinity binding sites (Kd 1.1 nM) and low number of the binding sites (30-40 sites/genome DNA). By gel filtration on Sephadex G-75 and molecular sieve HPLC, the binding protein was shown to have an Mr of about 20,000. These results indicate that the substance is a novel VB-C binding protein and suggest that it is a VB-receptor mediating the pleiotropic signal transmitted by VBs in S. virginiae.