The translation inhibitor microcin C7 (MccC7) is a low-molecular-weight, ribosomally encoded peptide antibiotic that is secreted by some strains of Enterobacteriaceae to kill their sensitive bacterial competitors. Microcin gene clusters include six genes, mccABCDEF, which encode proteins involved in maturation, export, and immunity. It was suggested that the sixth gene, MccF, encodes a specific self-immunity protein, making it resistant to the antibiotic microcin. The crystal structure of the MccF protein from Bacillus anthracis str. Ames was determined to 2.1 A. The asymmetric unit contains two molecules, which are associated into a homodimer. Fold analysis reveals close structural similarity to LD-carboxypeptidase, a serine peptidase from Pseudomonas aeruginosa (PDB id 2AUN). Sequence alignment with LD-carboxypeptidase and close homologs of the MccF protein shows conservation of the hydrolytic triad Ser-His-Glu, suggesting that the MccF protein may display the same activity.