Fig 1.
Conserved themes in protein secretion.
Gram-negative bacteria and mycobacterial secretion systems also have conserved sensing and regulatory mechanisms (bulleted list). Secretion systems of gram-negative bacteria and mycobacteria both employ feedback regulation (gray arrow) to control the amount of substrates that are produced or secreted (gradient arrow). Some gram-negative bacteria sense and respond to their external environments (lightning bolt). Gram-negative bacteria use porins for solute transport, while mycobacteria use PE/PPE proteins for solute transport. No transporter has yet been identified in the MOM of mycobacteria. CM, cytoplasmic membrane; OM, outer membrane; MOM, mycolic acid outer membrane.