Catalyzes the phosphorylation of the beta-carboxyl group of aspartic acid with ATP to yield 4-phospho-L-aspartate, which is involved in the branched biosynthetic pathway leading to the biosynthesis of amino acids threonine, isoleucine and methionine. ATP + L-aspartate = 4-phospho-L-aspartate + ADP Inhibited by threonine. kcat is 1500 min(-1). Thermostable. Amino-acid biosynthesis; L-lysine biosynthesis via DAP pathway; (S)-tetrahydrodipicolinate from L-aspartate: step 1/4. Amino-acid biosynthesis; L-methionine biosynthesis via de novo pathway; L-homoserine from L-aspartate: step 1/3. Amino-acid biosynthesis; L-threonine biosynthesis; L-threonine from L-aspartate: step 1/5. Heterotetramer consisting of 2 isoforms Alpha (catalytic and regulation) and of a homodimer of 2 isoforms Beta (regulation and thermostability). Belongs to the aspartokinase family.