Catalyzes the retro-aldol cleavage of 4-hydroxy-2-oxopentanoate to pyruvate and acetaldehyde. Is involved in the meta-cleavage pathway for the degradation of 3-phenylpropanoate. (S)-4-hydroxy-2-oxopentanoate = acetaldehyde + pyruvate Optimum pH is 6.25-6.75. Aromatic compound metabolism; 3-phenylpropanoate degradation. Interacts with MhpF. Presumably stereoselective for the 4S-enantiomer of 4-hydroxy-2-ketovalerate. Belongs to the 4-hydroxy-2-oxovalerate aldolase family.