Issue 7, 2022

Direct observation of humic acid-promoted hydrolysis of phytate through stabilizing a conserved catalytic domain in phytase

Abstract

As a potential phosphorus (P) pool, the enzymatic hydrolysis of organic phosphorus (Po) is of fundamental importance due to the release of bioavailable inorganic phosphate (Pi) for agronomic P sustainability. However, little is known about the role of soil organic matter (SOM) in the hydrolysis process of phytate by phytase and the subsequent chemical behaviors involving the hydrolysis product (Pi) at different soil interfaces. Here, by using liquid-cell atomic force microscopy (AFM), we present a model system to in situ quantify the nucleation kinetics of phytase-released Pi when precipitating with representative soil multivalent cations (Ca2+/Fe3+) on typical soil mineral/organic interfaces in the presence/absence of humic acid (HA), which involves complex phytase–interface–HA interactions. We observed that a higher HA concentration resulted in a faster nucleation rate of amorphous calcium/iron phosphate (ACP/AIP) on bare and organically-coated (–OH/–COOH) mica surfaces compared with the HA-free control. Besides, the nucleation rate of ACP/AIP induced by organic interfaces was much more significant than that induced by clay mineral interfaces. By combining enzyme activity/stability experiments and AFM-based PeakForce quantitative nanomechanical mapping (PF-QNM) measurements, we directly quantified the contribution of noncovalent phytase–HA interaction to the increase in enzymatic activity from complex phytase–interface–HA interactions. Furthermore, the direct complexation of phytase–HA resulted in the stabilization of a conserved active catalytic domain (ACD) in phytase through the enhanced formation of both an ordered, stereochemically-favored catalytic domain and an unordered non-catalytic domain, which was revealed by Raman secondary structure determination. The results provide direct insights into how HA regulates the catalytic activity of phytase controlling Po fates and how soil interfaces determine the behaviors of released Pi to affect its availability, and thereby contribute to P sustainability in soils.

Graphical abstract: Direct observation of humic acid-promoted hydrolysis of phytate through stabilizing a conserved catalytic domain in phytase

  • This article is part of the themed collection: Geochemistry

Supplementary files

Article information

Article type
Paper
Submitted
17 feb. 2022
Accepted
16 jun. 2022
First published
19 jun. 2022

Environ. Sci.: Processes Impacts, 2022,24, 1082-1093

Direct observation of humic acid-promoted hydrolysis of phytate through stabilizing a conserved catalytic domain in phytase

X. Ge, W. Zhang, C. V. Putnis and L. Wang, Environ. Sci.: Processes Impacts, 2022, 24, 1082 DOI: 10.1039/D2EM00065B

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