Involved in the degradation of ectoine, which allows H.elongata to utilize ectoine as both a carbon and a nitrogen source for growth. Probably catalyzes the conversion of L-2,4-diaminobutyrate (DABA) to L-aspartate beta-semialdehyde (ASA) by transamination with 2-oxoglutarate. 2-oxoglutarate + L-2,4-diaminobutanoate = L-aspartate 4-semialdehyde + L-glutamate Deletion mutant is impaired in growth on ectoine as a sole carbon source. DoeD and EctB both catalyze the same transamination reaction between L-aspartate 4-semialdehyde and L-2,4-diaminobutanoate coupled to the 2-oxoglutarate/L-glutamate pair. This reversible reaction is part of both, ectoine biosynthesis and ectoine degradation. Belongs to the class-III pyridoxal-phosphate-dependent aminotransferase family.