Pullulanase: model protein substrate for the general secretory pathway of gram-negative bacteria

Pullulanase of Klebsiella oxytoca is one of a wide variety of extracellular proteins that are secreted by Gram-negative bacteria by the complex main terminal branch (MTB) of the general secretory pathway. The roles of some of the 14 components of the MTB are now becoming clear. In this review it is proposed that most of these proteins form a complex, the secretion, that spans the cell envelope to control the opening and closing of channel in the outer membrane. Progress toward the goal of testing this model is reviewed.