Probably involved in bile acid degradation (Probable). In vitro, when associated with the ChsH1/ChsH2 hydratase, catalyzes the retroaldol cleavage of 17-hydroxy-3-oxo-4-pregnene-20-carboxyl-CoA (17-HOPC-CoA), forming androst-4-ene-3,17-dione and propionyl-CoA (PubMed:31209106). The in vivo substrate is probably a closely analogous bile acid degradation metabolite (Probable). 17-hydroxy-3-oxochol-4-en-22-oyl-CoA = androst-4-ene-3,17-dione + propanoyl-CoA kcat is 7.1 sec(-1). Homodimer (PubMed:31209106). Interacts with the ChsH1/ChsH2 hydratase via the DUF35 C-terminal region of ChsH2 (ChsH2-DUF35) (PubMed:31209106). Belongs to the thiolase-like superfamily.