PURIFICATION AND CHARACTERIZATION OF VIRGINIAE BUTANOLIDE C-BINDING PROTEIN, A POSSIBLE PLEIOTROPIC SIGNAL-TRANSDUCER IN STREPTOMYCES VIRGINIAE

Abstract

Virginiae butanolide C (VB-C) is an autoregulator which triggers virginiamycin production in Streptomyces virginiae. A new binding assay with tritium-labeled VB-C analogue (2, 3-cis-2-(1'hydroxy-[6', 7'-³H]heptyl)-3-(hydroxymethyl)butanolide) was developed and a specific VB-C binding protein was purified to homogeneity from crude extracts of S. virginiae by ammonium sulfate fractionation, DEAE-Sephacel and Sephadex G-100 column chromatographies, hydrophobic HPLC on phenyl 5PW and native polyacrylamide gel electrophoresis. The VB-C binding protein showed an apparent M_r of 35, 800 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and M_r of 26, 000 - 44, 000 on native molecular sieve HPLC, indicating the monomeric nature of the binding protein. The binding protein efficiently bound to a VB affinity column and eluted specifically by VB-C, which confirmed the specific nature of the binding protein. The binding activity decreased by 40% in the presence of genomic DNA from S. virginiae, indicating interaction between the VB-C binding protein and the DNA.