How many signal peptides are there in bacteria?

Area of Science:

• Proteomics
• Genomics
• Molecular Biology

Background:

• High-throughput identification of protein N-termini is crucial for accurate genome annotation.
• Signal peptides determine protein localization (cytoplasmic vs. extracytoplasmic).
• Existing prediction tools have limitations in accurately identifying signal peptides.

Purpose of the Study:

• To investigate the utility of proteogenomics for identifying signal peptides in Escherichia coli K-12.
• To compare proteogenomic findings with existing experimental data and computational predictions.
• To refine estimates of the proportion of E. coli proteins containing signal peptides.

Main Methods:

• Proteogenomic analysis using mass spectrometry to identify protein N-termini.
• Comparison of experimentally determined N-termini with in silico predictions (SignalP, Phobius).
• Application of filters for peptide length, hydrophobic patch, and cleavage sites to validate signal peptides.

Main Results:

• A single proteogenomics experiment identified over a third of experimentally determined signal peptides.
• Confirmed 31 additional predicted signal peptides, primarily in known exported proteins.
• Proteogenomic analysis and updated SignalP predictions suggest only ~10% of E. coli proteins possess signal peptides, half of prior estimates.

Conclusions:

• Proteogenomics is a powerful approach for high-throughput signal peptide identification and genome annotation refinement.
• The study significantly revises the estimated prevalence of signal peptides in E. coli.
• Validated filtering criteria effectively reduce false positives in signal peptide identification.