Catalyzes the condensation of (S)-aspartate-beta-semialdehyde [(S)-ASA] and pyruvate to 4-hydroxy-tetrahydrodipicolinate (HTPA). L-aspartate 4-semialdehyde + pyruvate = (2S,4S)-4-hydroxy-2,3,4,5-tetrahydrodipicolinate + H(+) + H2O Optimum pH is 8.0. At pH 9.0 or above, only 30% activity is observed. Optimum temperature is 37 degrees Celsius. The activity decreases slowly when temperatures are reduced from 37 degrees Celsius while the drop in activity is relatively more rapid when temperatures are raised above 37 degrees Celsius. In this case, the activity reduces to almost 30% at 52 degrees Celsius. Amino-acid biosynthesis; L-lysine biosynthesis via DAP pathway; (S)-tetrahydrodipicolinate from L-aspartate: step 3/4. Homodimer. Belongs to the DapA family. Was originally thought to be a dihydrodipicolinate synthase (DHDPS), catalyzing the condensation of (S)-aspartate-beta-semialdehyde [(S)-ASA] and pyruvate to dihydrodipicolinate (DHDP). However, it was shown in E.coli that the product of the enzymatic reaction is not dihydrodipicolinate but in fact (4S)-4-hydroxy-2,3,4,5-tetrahydro-(2S)-dipicolinic acid (HTPA), and that the consecutive dehydration reaction leading to DHDP is not spontaneous but catalyzed by DapB.