Bacteria have an important issue to deal with when assembling large protein complexes that span the cell envelope; how to get them through the peptidoglycan layer? Peptidoglycan, or PG, is a covalently linked, giant polymer that completely surrounds the cell and provides protection from high internal turgor pressures. PG has a mesh size of approximately 50 kDa, which is much smaller than the megadalton sizes of many of the protein complexes that pass through it. We are interested in understanding how bacteria cope with this problem, which impacts all motility and secretion systems that traverse the cell envelope.
In the type IV pilus system there is a protein called FimV that contains a PG-binding motif. Our work to date suggests that FimV is a member of the inner membrane PilMNOP complex and that it is involved in assembly of the outer membrane subcomplex that allows pilus to exit the cell. We have also identified two PG enzymes, a PBP (penicillin-binding protein) and the other an amidase, that are required for the correct assembly of type IV pilus and type II secretion systems.