Catalyzes reversively the conversion of L-aspartate beta-semialdehyde (ASA) to L-2,4-diaminobutyrate (DABA) by transamination with L-glutamate. 2-oxoglutarate + L-2,4-diaminobutanoate = L-aspartate 4-semialdehyde + L-glutamate Amine and polyamine biosynthesis; ectoine biosynthesis; L-ectoine from L-aspartate 4-semialdehyde: step 1/3. Belongs to the class-III pyridoxal-phosphate-dependent aminotransferase family.