TABLE 5.
Additional extracellular proteins in mutant B. subtilis strainsa
| Protein | Function or similarity | Export signalb | SPase | Retention signalc | Mediumd |
|---|---|---|---|---|---|
| B. subtilis Δlgt | LB | ||||
| FeuA | Iron-binding protein | Lipo | SPase II | (lipid) | LB |
| FhuD | Ferrichrome-binding protein | Lipo | SPase II | (lipid) | LB |
| MsmE | Manganese-binding protein | Lipo | SPase II | (lipid) | LB |
| OpuAC | Glycine-betaine-binding protein | Lipo | SPase II | (lipid) | PS |
| PbpC | Penicillin-binding protein 3 | Lipo | SPase II | (lipid) | LB, PS |
| RbsB | Ribose-binding protein | Lipo | SPase II | (lipid) | LB |
| YfiY | Iron(III)-binding protein | Lipo | SPase II | (lipid) | LB, PS |
| YodJ | d-Alanyl-d-alanine carboxypeptidase | Lipo | SPase II | (lipid) | LB |
| YusA | Putative part of the S-box regulon | Lipo | SPase II | (lipid) | LB |
| YxeB | Putative binding protein | Lipo | SPase II | (lipid) | LB, PS |
| B. subtilis ΔwprA | |||||
| YwsB | Similar to unknown proteins of B. subtilis | Sec | SPase I | − | LB |
All proteins listed were identified in the medium of mutant B. subtilis strains but not seen in the medium of the parental strain, 168 (as listed in Tables 1 and 2). Proteins were identified by 2D PAGE and subsequent MALDI-TOF mass spectrometry and/or N-terminal peptide sequencing as described by Antelmann et al. (5, 6). Putative signal peptides, SPase I or SPase II cleavage sites, transmembrane domains, and cell wall-binding domains were predicted as described by Tjalsma et al. (129) and Jongbloed et al. (51).
Identified transient export signals are Sec-type signal peptides (Sec) and lipoprotein signal peptides (Lipo).
Identified retention signals present in the mature part of the protein after processing by specific SPases are only lipid modifications (lipid). It should be noted that in the lgt mutant strain, the lipid retention signal is not attached to lipoprotein precursors. Furthermore, the YwsB protein, despite the absence of known cell wall-binding repeats (−), is retained in the cell wall of parental B. subtilis cells.