FIG. 7.

Steps of the type I secretion pathway. The model shown focuses on the functions of different regions of HasA in the assembly dynamics of the tripartite TolC-HasD-HasE system. (Step 1) Outer membrane (OM) TolC is recruited to HasDE only when HasA interacts with the ABC protein HasD (IM, inner membrane). These primary interactions between HasD and newly synthesized HasA are driven by linear sites which are sequentially exposed on the unfolded molecules during or soon after protein translation. (Step 2) The secondary interaction between HasD and HasA via C-terminal signaling induces ATP hydrolysis and separation of TolC to its preengagement state.