An ATP-independent periplasmic chaperone, decreases protein aggregation and helps protein refolding. Binds substrate over a large region. Protect proteins in vitro against tannin inactivation; tannins have antimicrobial activity. Overexpression enhances the stability of otherwise unstable periplasmic proteins (PubMed:21317898). Homodimer. Has an elongated cradle shape. Belongs to the CpxP/Spy family.