Tripartite efflux pumps and the type I secretion system of
Gram-negative bacteria are large protein complexes that span
the entire cell envelope. These complexes expel antibiotics and
other toxic substances or transport protein toxins from bacterial
cells. Elucidating the binary and ternary complex structures
at an atomic resolution are crucial to understanding the
assembly and working mechanism. Recent advances in cryoelectron
microscopy along with the construction of chimeric
proteins drastically shifted the assembly models. In this review,
we describe the current assembly models from a historical
perspective and emphasize the common assembly mechanism
for the assembly of diverse tripartite pumps and type
I secretion systems.