Processing of the N termini of nascent polypeptide chains requires deformylation prior to methionine removal

Area of Science:

• Molecular Biology
• Biochemistry
• Microbiology

Background:

• Bacterial protein synthesis initiates with N-formyl-methionine.
• Processing of this N-formyl-methionine is crucial for nascent polypeptide elongation.
• Previous assumptions about the order of N-formyl group removal and methionine cleavage were based on limited evidence.

Purpose of the Study:

• To definitively determine the requirement of N-formyl group removal prior to methionine cleavage by methionine aminopeptidase.
• To characterize the substrate specificity of Salmonella typhimurium methionine aminopeptidase.
• To confirm the physiological role of peptide deformylase in vivo.

Main Methods:

• In vitro enzymatic assays using Salmonella typhimurium methionine aminopeptidase.
• Development of a sensitive and quantitative assay for enzyme activity.
• Expression of a reporter protein in a bacterial strain deficient in peptide deformylase.

Main Results:

• Salmonella typhimurium methionine aminopeptidase was found to be completely inactive against N-formyl-methionyl peptides in vitro.
• Detailed substrate specificity of methionine aminopeptidase was elucidated.
• A reporter protein lacking peptide deformylase activity retained its N-formyl group, confirming the enzyme's in vivo function.

Conclusions:

• N-formyl group removal by peptide deformylase is a prerequisite for methionine cleavage by methionine aminopeptidase.
• This sequential processing is essential for proper bacterial protein synthesis.
• The study provides conclusive evidence for the necessity of peptide deformylase in vivo.