Poly-γ-glutamate depolymerase of Bacillus subtilis:: production, simple purification and substrate selectivity

The Bacillus subtilis pgdS gene, which is located at the immediate downstream of the pgs operon for poly-gamma-glutamate (PGA) biosynthesis, encodes a PGA depolymerase. The pgdS gene product shows the structural feature of a membrane-associated protein. The mature forrn of the gene product, identified as a B. subtilis extracellular protein, was produced in Escherichia coli clone cells. Since the mature PGA depolymerase has been modified with the histidine-tag at its C-terminus, it could be simply purified by metal-chelating affinity chromatography. This purified enzyme digested PGAs from B. subtilis (D-glutamate content, 70%) and from Bacillus megaterium (30%) in an endopeptidase-like fashion. In contrast, PGA from Natrialba aegyptiaca, which consists only of L-glutamate, was resistant to the enzyme, suggesting that, unlike fungal PGA endo-depolymerases, the bacterial enzyme recognizes the D-glutamate unit in PGA. (C) 2003 Elsevier B.V. All rights reserved.