Component of the spanin complex that disrupts the host outer membrane and participates in 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. Host outer membrane disruption is possibly due to local fusion between the inner and outer membrane performed by the spanin complex (By similarity). Interacts (via C-terminus) with the spanin outer lipoprotein subunit (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).