Signal sequence directs localized secretion of bacterial surface proteins Carlsson, F. et al. Nature 442, 943–946 (2006)
In bacteria, the presence of a signal sequence at the amino terminus of a nascent protein tags this protein for secretion across the cytoplasmic membrane. Secretion is not uniform, however, and some bacterial cell-surface proteins show distinct localization patterns. What determines this localized secretion? Carlsson et al. suggest that the answer lies in the signal sequence. They examined the secretion of two Streptococcus pyogenes proteins that are known to have different localization patterns — the M protein localizes to the septum whereas PrtF localizes to the old poles of growing cells. The signal sequences of these two proteins were swapped and the localization of the hybrid proteins was analysed using quantitative immunogold electron microscopy. It was shown that the signal sequence of the M protein directs secretion to the septum (perhaps promoting binding of the M protein to the cell division complex) and the signal sequence of PrtF directs secretion to the old poles. Work to determine the exact motifs responsible is ongoing.
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