The evolving story of AtzT, a periplasmic binding protein.

Atrazine is an s‐triazine‐based herbicide that is used in many countries around the world in many millions of tons per year. A small number of organisms, such as Pseudomonas sp. strain ADP, have evolved to use this modified s‐triazine as a food source, and the various genes required to metabolize atrazine can be found on a single plasmid. The atomic structures of seven of the eight proteins involved in the breakdown of atrazine by Pseudomonas sp. strain ADP have been determined by X‐ray crystallography, but the structures of the proteins required by the cell to import atrazine for use as an energy source are still lacking. The structure of AtzT, a periplasmic binding protein that may be involved in the transport of a derivative of atrazine, 2‐hydroxyatrazine, into the cell for mineralization, has now been determined. The structure was determined by SAD phasing using an ethylmercury phosphate derivative that diffracted X‐rays to beyond 1.9 Å resolution. 'Native' (guanine‐bound) and 2‐hydroxyatrazine‐bound structures were also determined to high resolution (1.67 and 1.65 Å, respectively), showing that 2‐hydroxyatrazine binds in a similar way to the purportedly native ligand. Structural similarities led to the belief that it may be possible to evolve AtzT from a purine‐binding protein to a protein that can bind and detect atrazine in the environment. [ABSTRACT FROM AUTHOR]