Developing osmolytes as nano-probes of biopolymer surfaces, interfaces, and conformational changes

We report novel quantitative studies of the preferential interactions of urea and the osmolytes glycine betaine (GB), trimethylamine-N-oxide (TMAO), and trehalose with biopolymer or amino acid surfaces. The principal conclusions of these analyses are that urea accumulates at polar amide surface and GB is excluded primarily from anionic surface of biopolymers. We quantify the extent of interaction of urea and GB with these surfaces per unit of water accessible biopolymer surface area (ASA). We show that urea is accumulated at polar amide surface of short amino acid oligomers (though to a slightly smaller extent than at biopolymer surface). We quantify the interactions of the above four solutes with native bovine serum albumin (BSA), and study their interactions with small solutes. We quantify the concentration dependent stabilization by GB, TMAO and trehalose of two proteins---the lac repressor DNA binding domain and an alanine based alpha-helical peptide. Studies with BSA provide a measure of solute interactions with charged (29%) and polar (18%; predominantly polar amide, 15%) biopolymer surface. Studies of lac repressor unfolding provide an equivalent measure of solute interactions with its nonpolar surface (73%) and polar amide surface (16%). Solute effects on unfolding the alpha-helical peptide measure the interactions of solutes primarily with polar amide surface (∼56%). This combination of solutes and biopolymer surfaces defines the behavior of urea and GB, and lays the foundation for developing TMAO and trehalose as probes for characterizing structural changes during biopolymer processes. The solute nano-probes are complementary to other structural methods like crystallography and NMR. Recent publications from this laboratory document the use of urea and GB in investigating coupled folding and interface formation in lac repressor-lac operator binding and in steps of RNA polymerase-promoter interactions that lead to open complex formation during transcription initiation.; We also report preliminary biopolymer surface interaction studies of three other nonelectrolyte solutes, glycerol, proline, and sarcosine, and three salts, potassium glutamate, ammonium sulfate, and potassium chloride.