Abstract

Intrinsically Disordered Proteins (IDPs), represent a challenge to the classic static conception of protein structure and function. Late Embryogenesis Abundant (LEA) proteins are IDPs that mediate water interactions in seeds. The interactions between a protein’s sequence of amino acids and its solvent drive protein folding. Group1 LEA proteins have an unusually high proportion of alanine, lysine, and glycine and we hypothesized that this unusual composition might cause LEA proteins to change conformation in response to salt concentration. To test whether individual amino acids differ in their tendency to associate with solvent as salt concentration changes, we calculated Half-Sphere Exposures of each amino acid from NMR Protein Data Bank files and plotted them as a function of the solvent salt concentration. We found that the unusual amino acid composition found in LEA proteins does not predict a greater response to changes in salt content. However, we found that different segments of the proteins had significantly different variances in the salt-sensitivity of solvent exposure of the amino acids. Interestingly, 12 amino acids showed a significant decrease in Half Sphere Exposure as salt concentration increased, which could indicate an overall loosening of proteins in high salt solutions. Overall, our results suggest that: uniformity in response to salt concentration may be important in LEA function and; solvent salt concentration is an important determinant of solvent exposure and hence protein structure. This may have implications for the solvents used to study proteins in the laboratory.