Figure 6. Impact of signal peptides and post-translational modifications on trafficking through the general Sec or aSec system.
A signal sequence with a relatively strong Sec avoidance motif is indicated in cyan, and signal sequences that can support transport by the general Sec system are indicated in red. A: In most streptococci, the aSec locus encodes four or more putative glycosyl transferases, and the SRR glycoprotein signal peptide is not optimal for general Sec transport. B: GspB variants with one or more substitutions of critical glycine residues in the signal peptide H region, or wild-type Fap1, may be inefficiently transported by the general Sec system (dashed line indicates transport of partially or incorrectly glycosylated substrates). C: In staphylococci, the aSec locus includes just the core GtfA/B glycosyl transferase, and the SRR glycoprotein signal peptide can facilitate transport via either the Sec or aSec pathway.