Elucidating the Physical and Chemical Structural Changes of Proteins on Clay Mineral Surfaces using Large-scale Molecular Dynamics Simulations in Tandem with NMR Spectroscopy

Carbon cycling among the three major Earth's pools, i.e., atmosphere, terrestrial systems and oceans, has received increased attention because the concentration of CO2 in the atmosphere has increased significantly in recent years reaching concentrations greater than 400 ppm that have never been recorded before, warming the planet and changing the climate. Within the terrestrial system, soil organic matter (SOM) represents an important sub-pool of carbon. The associations of SOM with soil mineral interfaces and particles, creating micro-aggregates, are believed to regulate the bioavailability of the associated organic carbon by protecting it from transformations and mineralization to carbon dioxide. Nevertheless, the molecular scale interactions of different types of SOM with a variety of soil minerals and the controls on the extent and rate of SOM transformation and mineralization are not well documented in the current literature. Given the importance of SOM fate and persistence in soils and the current knowledge gaps, the application of atomistic scale simulations to study SOM/mineral associations in abiotic model systems offers rich territory for original and impactful science. Molecular modeling and simulation of SOM is a burgeoning and challenging avenue for aiding the characterization of these complex compounds and chemical systems and for studying their interactions in self-assembled aggregates composed of different organic matter compounds and with mineral surfaces of different types and common in soils, which are thought to contribute to their reactive properties including recalcitrance potential and resistance to mineralization. Here, we will discuss our large-scale molecular dynamics simulation efforts to explore the interaction of proteins with clay minerals (i.e., phyllosilicates such as kaolinite, smectite and micas), including the potential physical and chemical structural changes of proteins, protein adsorption by polar and permanently charged mineral surfaces and variably charged edges, and the potential role of amphiphilic proteins in providing adsorptive layers for SOM-mineral interfaces. Our efforts at characterizing these systems through combined modeling and simulation and NMR will also be discussed.