Structural and Biophysical Characterization of EppA

Abstract

Ethylenediaminetetraacetate (EDTA) is an anthropogenic aminopolycarboxylate chelator whose widespread use, combined with its chemical stability, has led to its persistence in the environment as metal-chelate complexes. Being a ubiquitous environmental pollutant, finding a means by which we can clean up EDTA pollution in the environment is imperative. One way to remove EDTA is through bioremediation in which a unique microbial process is harnessed, such as the epp-emo pathway from Chelativorans sp. BNC1. Although the enzymatic pathway has been characterized, the biophysical mechanism of the associated ABC-type transporter is incomplete thus far. To these ends, we characterized the relationship between the structure and function of EppA, an EDTA-binding periplasmic protein. To obtain the molecular structure of EppA, single-crystal X-ray diffraction was used. Molecular docking was used to dock EDTA and chemically related chelators to the structure, showing that they bind with EppA's putative ligand-binding cleft. To confirm their binding experimentally, isothermal titration calorimetry was performed. EppA's high affinity for chemically similar chelators suggests that other proteins further down the catabolic pathway may be useful for degrading a wider range of chelators than previously thought or can otherwise be engineered to do so. This makes the epp-emo EDTA-degradation pathway of Chelativorans sp. BNC1 a powerful tool for combating pollution.