Part of a type II secretion system (T2SS, formerly general secretion pathway, GSP) for the export of folded proteins across the outer membrane (Probable). This subunit forms the outer membrane channel (Probable). Forms a cylindrical channel with 15 subunits, each of which interacts with the surrounding pilotin AspS2 proteins (also called GspS-beta) (PubMed:29632366). Interacts with inner cell membrane protein GspC2 in the periplasm (PubMed:21931548). Forms multimers in the outer membrane (PubMed:22585966). The isolated N0 domain forms dimers that self-assemble into rings (PubMed:23820381). Some protein is also found in the cell inner membrane, the inner membrane protein does not form multimers and is unstable (PubMed:22585966). Most of the protein is in the periplasm which it traverses to contact proteins of the cell inner membrane (Probable). The N0 region interacts in the periplasm with GspC (PubMed:21931548). The S domain interacts with pilotin AspS2 (PubMed:29632366). The N0, N1, N2 and N3 domains are periplasmic, while the secretin and S domains form a channel that is partially inserted in the outer membrane. The cap gate extends out on the extracellular side of the channel partially closing the channel. The secretin domain forms a double beta-barrel structure; the outer barrel has an outer diameter of about 110 Angstroms while the inner barrel forms the central gate with a small pore in the closed state (By similarity). Severely disrupts assembly and function of T2SS-beta. Encoded in a type II secretion system (T2SS-beta); this strain encodes 2 T2SS but only this one (beta) is expressed under standard laboratory conditions. Belongs to the bacterial secretin family. GSP D subfamily.