Hierarchical Reactivity of Enzyme-Mediated Phosphorus Recycling from Organic Mixtures by Aspergillus niger Phytase.

Biological recycling of inorganic phosphorus (Pi) from organic phosphorus (Po) compounds by phosphatase-type enzymes, including phytases, is an important contributor to the pool of bioavailable P to plants and microorganisms. However, studies of mixed-substrate reactions with these enzymes are lacking. Here, we explore the reactivity of a phytase extract from the fungus Aspergillus niger toward a heterogeneous mixture containing, in addition to phytate, different structures of environmentally relevant Po compounds such as ribonucleotides and sugar phosphates. Using a high-resolution liquid chromatography-mass spectrometry method to monitor simultaneously the parent Po compounds and their by-products, we captured sequential substrate-specific evolution of Pi from the mixture, with faster hydrolysis of multiphosphorylated compounds (phytate, diphosphorylated sugars, and di- and tri-phosphorylated ribonucleotides) than hydrolysis of monophosphorylated compounds (monophosphorylated sugars and monophosphorylated ribonucleotides). The interaction mechanisms and energies revealed by molecular docking simulations of each Po compound within the enzyme's active site explained the substrate hierarchy observed experimentally. Specifically, the favorable orientation for binding of the negatively charged phosphate moieties with respect to the positive potential surface of the active site was important. Collectively, our findings provide mechanistic insights about the broad but hierarchical role of phytase-type enzymes in Pi recycling from the heterogeneous assembly of Po compounds in agricultural soils or wastes.