Component of the type II secretion system inner membrane complex required for the energy-dependent secretion of extracellular factors such as proteases and toxins from the periplasm. Type II secretion system is composed of four main components: the outer membrane complex, the inner membrane complex, the cytoplasmic secretion ATPase and the periplasm-spanning pseudopilus (By similarity). Homodimer (By similarity). Interacts with GspE and GspL components (By similarity). Silenced by the DNA-binding protein H-NS under standard growth conditions. Part of a cryptic operon that encodes proteins involved in type II secretion machinery in other organisms, but is not expressed in strain K12. Belongs to the GSP F family.