Part of the Tol-Pal system, which plays a role in outer membrane invagination during cell division and is important for maintaining outer membrane integrity. The Tol-Pal system is composed of five core proteins: the inner membrane proteins TolA, TolQ and TolR, the periplasmic protein TolB and the outer membrane protein Pal. They form a network linking the inner and outer membranes and the peptidoglycan layer. More than twofold more abundant in the small cell variant (SCV) stage than in the large cell variant (LCV) stage (at protein level). LCVs are more metabolically active than SCVs. Belongs to the TolB family.