Soil aggregates stability is evidently enhanced by super-binding of the N-terminal disordered tail of glomalin to soil minerals

Abstract

Glomalin-related soil protein (GRSP) extracted from soil is considered crucial for the formation and stability of soil aggregates. However, due to limitations in extraction purity and interference from co-extracted products, the actual contribution of pure glomalin produced by arbuscular mycorrhizal fungi (AMF) to soil structure improvement and its specific mechanism of action remain elusive. Here, genetic engineering and cryo-electron microscopy (cryo-EM) are introduced to obtain purified glomalin and to determine its homo-tetradecamer structure. This allowed investigations of the effect of pure glomalin on soil aggregate stability and the specific glomalin-mineral interaction mechanism. The results showed that addition of glomalin significantly enhanced the formation of soil water-stable aggregates and soil macroaggregates. This enhancement was primarily attributed to the strong binding of glomalin to soil minerals, as evidenced by single molecule force spectroscopy (SMFS) and attenuated total reflectance-Fourier transform infrared spectrum (ATR-FTIR) experiments. Glomalin structural analysis, comparison of its amino sequence alignment with that of Escherichia coli heat shock protein 60 (E. coli Hsp60) and mineral binding experiments with several glomalin related mutants highlighted that the N-terminus disordered tail of glomalin composed of ∼39 amino acids were crucial for the glomalin super binding ability. These findings advance the understanding of glomalin's intrinsic mechanism for improving soil structure and open the opportunity for mass production of this ecologically important protein as a soil amendment.