Abstract
Adenylate isopentenyl transferase (IPT) catalyzes the first step of cytokinin biosynthesis, the addition of isopentenyl group of dimethylallyl pyrophosphate to N6 position of adenine nucleotide. We have determined the crystal structure of agrobacterial IPT, tzs protein, at 2.3 angstrom resolution. Tzs protein comprises 2 structural domains. N-terminal domain has a nucleotide binding motif, p-loop (residues 8-15), and is structurally homologous to p-loop containing nucleoside triphosphate hydrolase family. On the other hand, C-terminal domain is composed of 5 helices. These 2 domains form active-site channel at the interface between them. AMP molecule, which is the substrate in tzs protein, binds to one entrance of the channel regardless of no addition of AMP molecule in the crystallization conditions, whereas there is no interaction between AMP and p-loop.
