Mutational analysis of Bacillus subtilis glutamine phosphoribosylpyrophosphate amidotransferase propeptide processing

Glutamine phosphoribosylpyrophosphate amidotransferase from Bacillus subtil is is a member of an N-terminal nucleophile hydrolase enzyme superfamily, s everal of which undergo autocatalytic propeptide processing to generate the mature active enzyme. A series of mutations was analyzed to determine whet her amino acid residues required for catalysis are also used for propeptide processing. Propeptide cleavage was strongly inhibited by replacement of t he cysteine nucleophile and two residues of an oxyanion hole that are requi red for glutaminase function. However, significant propeptide processing wa s retained in a deletion mutant with multiple defects in catalysis that was devoid of enzyme activity. Intermolecular processing of noncleaved mutant enzyme subunits by active wild-type enzyme subunits was not detected in het ero-oligomers obtained from a coexpression experiment. While direct in vitr o evidence for autocatalytic propeptide cleavage was not obtained, the resu lts indicate that some but not all of the amino acid residues that have a r ole in catalysis are also needed for propeptide processing.