Abstract
The phytohormone cytokinin regulates plant growth and development. This hormone is also synthesized by some phytopathogenic bacteria, such as Agrobacterium tumefaciens, and is as a key factor in the formation of plant tumors. The rate-limiting step of cytokinin biosynthesis is catalyzed by adenosine phosphate-isopentenyltransferase (IPT). Agrobacterium IPT has a unique substrate specificity which enables it to increase trans-zeatin production by recruiting a metabolic intermediate of the host plants biosynthetic pathway.
We determined the crystal structures of Tzs, an IPT from Agrobacterium tumefaciens, complexed with substrate or its analogue. The structures provide a structural insight into the reaction mechanism and unique evolution of cytokinin biosynthesis.
A structure-based site-directed mutagenesis study of Tzs was used to identyfy the crucial amino acid residues, Asp173 and His214, which are responsible for differences in substrate specificity between plant and bacterial IPTs.
