A Step-Wise Method for Maximizing Protein Extraction from Different Soil Types.

Most organic N in soil is not present as intracellular proteins but rather as extracellular proteinaceous material that must be broken down and eventually converted to inorganic forms before it is available to plants.  The advent of metaproteomics provides a method for better understanding of the complexities of the degradation of extracellular proteinaceous materials, but requires a reliable method of protein extraction from the complex soil system.  The multi-step fractionation method for extracting proteins from soil is grounded in known interactions between proteins and the soil matrix.  This step-wise approach was developed to achieve quantitative extractions of proteins from the soil matrix, while minimizing alterations to the isolated proteins, by targeting and disrupting the range of bonding interactions (e.g., physical occlusion, hydrogen bonding, electrostatic interactions, hydrophobic bonds) between polypeptide chains and soil matrix components.  The goal was to identify a protein extraction method that will work for multiple types of soils with a range of physical and chemical properties.  Four different forest soils representing andisols and inceptisols, pH ranges from 3.6 to 7.0, and different clay content and mineralogy were used to test the step-wise extraction protocol.