Gold nanoparticle-based tool to study protein conformational variants: implications in hemoglobinopathy

The size of gold nanoparticles is shown here to gradually decrease if it is allowed to grow on a protein template, and the protein is subjected to unfolding by a nonionic denaturant. The correlation between size of the gold nanoparticle formed and the plasmon frequency observed remains linear, except at stages where protein folding intermediates are formed. Higher population of exposed tyrosine residues, number of sulfhydryl groups of the protein, and the overall exposition of the inner hydrophobic core may lead to the generation of smaller particles. The method provides a simple colorimetric sensing of protein conformation and has been tested for both nonheme and heme proteins (hemoglobin and bovine serum albumin). Similarly, protein variants with defects in folding (caused by subunit misassembly or mutation) can also be classified. Possible application of this approach in hemoglobinopathy (e.g., thalassemia carrier detection) is discussed in the text.