Structural characterization of dimeric murine aminoacylase III

Aminoacylase III (AAIII) plays an important role in deacetylation of acetylated amino acids and N-acetylated S-cysteine conjugates of halogenated alkenes and alkanes. AAIII, recently cloned from mouse kidney and partially characterized, is a mixture of tetramers and dimers. In the present work, AAIII dimers were purified and shown to be enzymatically active. Limited trypsinolysis showed two domains of ∼9 and 25 kDa. The three-dimensional structure of the dimer was studied by electron microscopy of negative stained samples and by single-particle reconstruction. A 16 Å resolution model of the AAIII dimer was created. It has an unusual, cage-like, structure. A realistic AAIII tetramer model was built from two dimers.