A typical system is comprised of 1 ABC and 2 IM. Only one system has been experimentally characterized, the LolCDE system of E. coli. Lipoproteins directed to the outer membrane are released from the inner membrane in an ATP-dependent manner through the formation of a complex with LolA, a periplasmic chaperone. The LolCDE complex catalyses the release of lipoproteins from the cytoplasmic membrane prior to their targeting to the outer membrane ( Pubmed : 10783239 ) . Since this complex is neither involved in export nor in import of molecules, it will constitute a new type of ABC system. Homologues of the LolCDE system have been found also in Gram-positive bacteria and archaea, and this suggests that the members of this family might be involved in a more general lipoprotein releasing mechanism common to all prokaryotes. In Agrobacterium tumefaciens, attachement of bacteria to host cells and virulence was found dependent on the integrity of the AttEFGH system ( Pubmed : 8752352 ) . The Streptococcus pneumoniae VexP system was found to influence the extracellular levels of the pep27 death peptide ( Pubmed : 10678168 ) . In Streptococcus mutans, the mutAB system affects mutacin production, morphology and competence. It is therefore probable that the activities of o228 systems are related to the cell surface.