THE MATURATION PATHWAY OF MICROCIN B17, A PEPTIDE INHIBITOR OF DNA GYRASE

The maturation pathway of microcin B17 (MccB17), a ribosomally synthes ized peptide antibiotic which inhibits DNA gyrase, has been characteri zed. Synthesis of MccB17 involves several steps beginning with the tra nslation of the MccB17 structural gene, mcbA, to yield a 69 amino acid precursor, preMccB17. Pre-MccB17 is then modified and folded by the a ction of three gene products, McbBCD, to yield proMccB17. Mutations in mcbA were isolated that permit modifications of the resulting mutant peptides, but prevent folding, suggesting that modification and foldin g are sequential steps. ProMccB17 is subsequently converted to MccB17 by removal of the N-terminal 26-amino-acid leader by a chromosomally e ncoded protease. Removal of the leader resulted in aggregation of the peptide, suggesting that the leader may function to maintain peptide s olubility during synthesis in the cell. Finally, polyclonal antibodies raised against MccB17 recognize both MccB17 and proMccB17, but do not recognize preMccB17. This demonstrates the dramatic structural change s that result from the modifications and has been used to distinguish intermediates in the steps of maturation.