Glomalin-related soil protein contains non-mycorrhizal-related heat-stable proteins, lipids and humic materials |
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Authors: | Adam W. Gillespie Fran L. Walley Andrew R.S. Ross Kai-Uwe Eckhardt Robert I.R. Blyth |
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Affiliation: | a Department of Soil Science, University of Saskatchewan, 51 Campus Drive, Saskatoon, Saskatchewan, Canada b Fisheries and Oceans Canada, Institute of Ocean Sciences, Ocean Sciences Division, 9860 West Saanich Road, Sidney, British Columbia, Canada c Institute for Land Use, University of Rostock, Justus von Liebig Weg 6, Rostock, Germany d Canadian Light Source Inc., University of Saskatchewan, 101 Perimeter Road, Saskatoon, Saskatchewan, Canada |
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Abstract: | Glomalin is reportedly a stable and persistent protein produced in copious quantities by mycorrhizal fungi and may be an important pool of organic N in soil. Glomalin-related soil protein (GRSP), however, is only operationally defined by its extraction method, and has been only poorly characterized at best. The goal of this study was to characterize the molecular structures within GRSP. Synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy and pyrolysis field-ionization mass spectrometry (Py-FIMS) revealed that GRSP contains a consortium of proteins along with many impurities. Employing proteomic techniques, we found that glomalin itself may be a thioredoxin-containing chaperone; however, no homologies with proteins or DNA of mycorrhizal origin were detected. Proteomics techniques further revealed that this fraction contains large amounts of soil-related heat-stable proteins and proteins of non-mycorrhizal origin. Results of this research show that the current extraction procedure that defines GRSP yields a mixture of compounds and thereby overestimates glomalin stocks when quantified using the Bradford assay. The chemical nature of glomalin has yet to be conclusively determined; it is unlikely that the chemical structure of glomalin can be elucidated from the mixture extracted as GRSP. Instead, an investigation into the specific biochemistry of immunoreactive assays currently used to define GRSP, followed by proteomic characterization of monoxenic mycorrhizal cultures may be required to advance our understanding of the chemical nature and agronomic significance of GRSP in soils. |
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Keywords: | Glomalin Soil proteins XANES Py-FIMS Proteomics |
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