RESUMO
Streptomyces murayamensis carries two aspartate kinase (AK) genes: one for the biosynthesis of lysine, threonine, and methionine, and the other (nspJ) contained in the biosynthetic gene cluster for the secondary metabolite, 4-hydroxy-3-nitrosobenzamide, for catalyzing the first reaction. AKs involved in the biosynthesis of amino acids are often regulated allosterically by the end products. In the present study, we characterized NspJ to investigate whether AKs involved in secondary metabolism were also allosterically regulated. NspJ was in α2ß2 and (α2ß2)2 heterooligomeric forms, and was insensitive to all the compounds tested including lysine, threonine, and methionine. The reduction in the activity following the removal of ammonium sulfate, which induced subunit dissociation, suggests that the ß subunit may be involved in stabilizing the structure of the α subunit in order to exhibit its activity. This study has provided the first example of a feedback-insensitive α2ß2-type AK, which is involved in the secondary metabolism.
