4-hydroxy-2-oxovalerate aldolase, N-terminal catalytic TIM barrel domain4-hydroxy 2-ketovalerate aldolase (Also known as 4-hydroxy-2-ketovalerate aldolase and 4-hydroxy-2-oxopentanoate aldolase (HOA)) converts 4-hydroxy-2-oxopentanoate to acetaldehyde and pyruvate, the penultimate step in the meta-cleavage pathway for the degradation of phenols, cresols and catechol. This family includes the Escherichia coli MhpE aldolase, the Pseudomonas DmpG aldolase, and the Burkholderia xenovorans BphI pyruvate aldolase. In Pseudomonas, the DmpG aldolase tightly associates with a dehydrogenase (DmpF ) and is inactive without it. HOA has a canonical TIM-barrel fold with a C-terminal extension that forms a funnel leading to the active site. This family belongs to the DRE-TIM metallolyase superfamily. DRE-TIM metallolyases include 2-isopropylmalate synthase (IPMS), alpha-isopropylmalate synthase (LeuA), 3-hydroxy-3-methylglutaryl-CoA lyase, homocitrate synthase, citramalate synthase, 4-hydroxy-2-oxovalerate aldolase, re-citrate synthase, transcarboxylase 5S, pyruvate carboxylase, AksA, and FrbC. These members all share a conserved triose-phosphate isomerase (TIM) barrel domain consisting of a core beta(8)-alpha(8) motif with the eight parallel beta strands forming an enclosed barrel surrounded by eight alpha helices. The domain has a catalytic center containing a divalent cation-binding site formed by a cluster of invariant residues that cap the core of the barrel. In addition, the catalytic site includes three invariant residues - an aspartate (D), an arginine (R), and a glutamate (E) - which is the basis for the domain name "DRE-TIM".