Involved in the degradation of glucose and galactose via the Entner-Doudoroff pathway. Catalyzes the reversible cleavage of 2-keto-3-deoxy-6-phosphogluconate (KDPG) and 2-keto-3-deoxygluconate (KDG) forming pyruvate and glyceraldehyde 3-phosphate or glyceraldehyde, respectively. It is also able to catalyze the reversible cleavage of 2-keto-3-deoxy-6-phosphogalactonate (KDPGal) and 2-keto-3-deoxygalactonate (KDGal). It is equally active with both D- and L-glyceraldehyde. 2-dehydro-3-deoxy-6-phospho-D-gluconate = D-glyceraldehyde 3-phosphate + pyruvate 2-dehydro-3-deoxy-6-phospho-D-galactonate = D-glyceraldehyde 3-phosphate + pyruvate kcat is 28.2 sec(-1) for KDG and 6.8 sec(-1) for KDGal. Extremely thermostable. Carbohydrate acid metabolism; 2-dehydro-3-deoxy-D-gluconate degradation; D-glyceraldehyde 3-phosphate and pyruvate from 2-dehydro-3-deoxy-D-gluconate: step 2/2. Homotetramer; dimer of dimers. The metabolic pathway in Sulfolobus species contrasts with the situation observed in other microorganisms where separate enzymes exist for the catabolism of the two sugars, glucose and galactose. Belongs to the DapA family. KDPG aldolase subfamily.