Structures of aminoglycoside acetyltransferase AAC(6′)-Ii in a novel crystal form: structural and normal-mode analyses

The aminoglycoside-modifying enzyme aminoglycoside 6′-N-acetyltransferase type Ii [AAC(6′)-Ii] has been crystallized with its cofactor coenzyme A in space group C222₁, with unit-cell parameters a = 71.5, b = 127.4, c = 76.9 Å and one physiologically relevant dimer species per asymmetric unit. The space group previously observed for this complex was P2₁2₁2₁, with two dimers per asymmetric unit. By comparing the six available protomer structures of the AAC(6′)-Ii–CoA complex, it has been possible to identify regions of plasticity within the protein. Normal-mode analysis of this complex suggests that this plasticity is not an artefact of crystal-packing forces, but that the region of the protomer that displays multiple conformations is intrinsically flexible. It is conjectured that the flexibility is relevant for the cooperative activity observed for the enzyme.