Mutational analysis of the glutamine phosphoribosylpyrophosphate amidotransferase pro-peptide.

Bacillus subtilis glutamine phosphoribosylpyrophosphate amidotransferase is synthesized as a pro-enzyme having an 11-amino acid leader. Maturation requires insertion of a [4Fe-4S] cluster and processing of the pro-peptide to expose an NH2-terminal active site cysteine residue. Point and deletion mutations were constructed in the leader region. These mutations affect processing and enzyme activities. Processing of the leader is dependent upon glutamic acid residues at positions -2 and -1 as well as Cys1. In addition, processing requires a pro-peptide longer than 3 residues. Function of the active site cysteine is dependent on pro-peptide processing. Enzyme purified from a pro-peptide deletion strain has activity and iron content that is comparable to the wild type. These results establish that the pro-peptide is not essential for enzyme maturation, but they leave unanswered the question of pro-peptide function.