GspLGspMGspF

GspLGspMGspF refers to the core inner membrane assembly formed by three components of the type II secretion system (T2SS) in many Gram-negative bacteria: GspL, GspM, and GspF. These proteins function together as a scaffold that links the energy-providing cytoplasmic components to the periplasmic secretion channel, enabling the transport of folded substrates across the cell envelope.

Structurally, GspF typically contains two transmembrane helices with periplasmic and cytoplasmic regions that interact with GspL and GspM. GspL has a cytoplasmic domain capable of binding the ATPase GspE, connecting the energy source to the secretion machinery, while GspM features transmembrane and periplasmic elements that help stabilize the complex and coordinate interactions with other components, such as the pseudopilus formed by GspG. Together, the GspL and GspM pair provides an anchor and interface for assembly, positioning GspF within the inner membrane.

Functionally, the GspLGspMGspF assembly acts as a transduction platform that couples ATP hydrolysis by GspE to the assembly and operation of the pseudopilus and the secretion channel. This arrangement coordinates substrate capture, pseudopilus extension, and passage through the outer membrane secretin GspD, facilitating efficient secretion of enzymes and toxins in many pathogenic bacteria.

Occurrence and evolution of this core module are widespread among diverse Gram-negative lineages, though the exact composition and stoichiometry can vary. Gene clusters encoding gspL, gspM, and gspF are commonly found adjacent to other T2SS components, reflecting their integrated role in the secretion apparatus. Ongoing structural and functional studies aim to further delineate the dynamic interactions within GspLGspMGspF and their impact on secretion efficiency and virulence.