Involved in cholesterol degradation. Catalyzes the retro-aldol cleavage of 4-hydroxy-2-oxohexanoate (HOHA) to pyruvate and propanal. Can also catalyze the cleavage of 4-hydroxy-2-oxopentanoate (HOPA) to pyruvate and acetaldehyde. The aldehydes produced by this reaction are directly channeled to the dehydrogenase HsaG. (S)-4-hydroxy-2-oxohexanoate = propanal + pyruvate (S)-4-hydroxy-2-oxopentanoate = acetaldehyde + pyruvate Homodimer. Forms an heterotetramer composed of two aldolase (HsaF) and two dehydrogenase (HsaG) subunits. Belongs to the 4-hydroxy-2-oxovalerate aldolase family.