Group 3 LEA Protein Model Peptides Suppress Heat-Induced Lysozyme Aggregation. Elucidation of the Underlying Mechanism Using Coarse-Grained Molecular Simulations

We investigated experimentally whether a short peptide, PvLEA-22, which consists of two tandem repeats of an 11-mer motif of Group 3 late embryogenesis abundant proteins, has a chaperone-like function for denatured proteins. Lysozyme was selected as a target protein. Turbidity measurements indicated that the peptide suppresses the heat-induced aggregation of lysozyme when added at a molar ratio of PvLEA-22/lysozyme >40. Circular dichroism and differential scanning calorimetry measurements confirmed that the lysozyme was denatured on heating but spontaneously refolded on subsequent cooling in the presence of the peptide. As a result, up to 80% of the native catalytic activity of lysozyme was preserved. Similar chaperone-like activity was also observed for a peptide with the same amino acid composition as PvLEA-22 but whose sequence is scrambled. To elucidate the underlying mechanism of the chaperone function of these peptides, we performed coarse-grained molecular dynamics simulations. This revealed that a denatured lysozyme molecule is shielded by several peptide molecules in aqueous solution, which acts as a physical barrier, reducing the opportunities for collision between denatured proteins. An important finding was that a peptide bound to the denatured protein is very rapidly replaced by another; due to such rapid exchange, peptide–protein contact time is very short, that is, on the order of ∼200 ns. Therefore, the peptide does not constrain the behavior of the denatured protein, which can refold freely.