Component of the spanin complex that disrupts the host outer membrane and causes cell lysis during virus exit. The spanin complex conducts the final step in host lysis by disrupting the outer membrane after holin and endolysin action have permeabilized the inner membrane and degraded the host peptidoglycans (By similarity). Homodimer; disulfide-linked. Interacts (via C-terminus) with RZ (via C-terminus). Part of the spanin complex which spans the entire periplasmic space. The spanin complex is composed of spanin, inner membrane subunit and spanin, outer membrane subunit (By similarity). Belongs to the lambdalikevirus o-spanin family.