Upon trypsinolysis, the 18 C-terminal residues of Escherichia coli peptide deformylase were removed but the resulting form exhibited full activity. Moreover, a mutant fms gene encoding the first 145 out of the 168 residues of the enzyme was able to complement a fms(Ts) strain and exhibited full activity. Upon progressive truncation up to residue 139, both activity and stability decreased up to complete inactivation. Mutagenesis of residues of the 138–145 region highlights the importance of Leu-141 and Phe-142. N-Terminal deletions were also carried out. Beyond two residues off, the enzyme showed a dramatic instability. Finally, NMR and thermostability studies of the full-length enzyme and comparison to the 1–147 form strongly suggest that the dispensable residues are disordered in solution.
