Structural insights into the Type II secretion nanomachine

► Type II secretion systems move folded proteins across the bacterial outer membrane. ► 3D structures of all major soluble domains in secretion system proteins have been solved. ► A gated outer membrane secretin allows for passage of secreted substrates. ► The secretin is connected to an energy-harvesting complex by a clamp protein. ► Specialized subunits initiate assembly of a pilus-like filament required for secretion.