Bacterial proteins with cleaved or uncleaved signal peptides of the general secretory pathway

J Proteomics. 2011 Dec 21;75(2):502-10. doi: 10.1016/j.jprot.2011.08.016. Epub 2011 Sep 5.

Abstract

Correct protein compartmentalization is a key step for molecular function and cell viability, and this is especially true for membrane and externalized proteins of bacteria. Recent proteomic reports of Bacillus subtilis have shown that many proteins with Sec-like signal peptides and absence of a transmembrane helix domain are still observed in membrane-enriched fractions, but further evidence about signal peptide cleavage or soluble protein contamination is still needed. Here we report a proteomic screening of identified peptides in culture filtrate, membrane fraction and whole cell lysate of Mycobacterium tuberculosis. We were able to detect peptide sequencing evidence that shows that the predicted signal peptide was kept uncleaved for several types of proteins such as mammalian cell entry (Mce) proteins and PE or PE-PGRS proteins. Label-free quantitation of all proteins identified in each fraction showed that the majority of these proteins with uncleaved signal peptides are, indeed, enriched in the Triton X-114 lipid phase. Some of these proteins are likely to be located in the inner membrane while others may be outer membrane proteins.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Outer Membrane Proteins / chemistry
  • Bacterial Outer Membrane Proteins / isolation & purification
  • Bacterial Outer Membrane Proteins / metabolism*
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / isolation & purification
  • Membrane Proteins / isolation & purification
  • Membrane Proteins / metabolism*
  • Mycobacterium tuberculosis / chemistry*
  • Mycobacterium tuberculosis / genetics
  • Protein Sorting Signals / genetics*
  • Protein Structure, Secondary
  • Secretory Pathway
  • Sequence Alignment
  • Serine Endopeptidases / metabolism

Substances

  • Bacterial Outer Membrane Proteins
  • Bacterial Proteins
  • Membrane Proteins
  • Protein Sorting Signals
  • Serine Endopeptidases
  • type I signal peptidase