The Staphylococcus aureus secretome - TI Pharma

Mapping the pathways to staphylococcal pathogenesis by comparative secretomics
translational protein export in E. coli, the cytoplasmic chaperone SecB has mainly been
implicated in post-translational protein targeting. Notably however, SecB is absent from the
sequenced Gram-positive bacteria, including S. aureus and B. subtilis. Most likely, ribosomenascent
chain complexes of S. aureus are thus targeted to the membrane by SRP, which, by
analogy to B. subtilis and E. coli will probably involve the SRP receptor FtsY. At the
membrane, the nascent preprotein will be directed to the translocation machinery. This
process is likely to be stimulated by negatively charged phospholipids (De Leeuw et al.,
2000), the Sec translocon (Bibi, 1998; De Leeuw et al., 2000) and/or the SecA protein (Bunai
et al., 1999). In this respect SecA may not only function as the translocation motor (see
below), but also as a chaperone for preprotein targeting (Herbort et al., 1999). While it has
been shown that Ffh is essential for growth and viability in E. coli and B. subtilis, this does
not seem to be the case in all bacteria. For example, Ffh, FtsY and scRNA are not essential in
Streptococcus mutans. In this organism the SRP is merely required for growth under stressful
conditions, such as low pH (