The Q-Rule: Pyroglutamate in Signal Peptidase I Substrates.

feature prominently in the human microbiome, as major colonizers of the gut and clinically relevant pathogens elsewhere. Here, we reveal a new specific feature in the otherwise widely conserved Sec/SPI (Sec translocase/signal peptidase I) pathway. In , but not the entire FCB group or related phyla, signal peptide cleavage exposes N-terminal glutamine residues in most SPI substrates.