Mercuration of apo-α-lactalbumin: binding of Hg²⁺followed by protein-mediated nanoparticle formation

Abstract

Nanoparticles and nanocrystals of mercury are formed when Hg 2+ salt reacts with apo-a-lactalbumin (apoa-LA). Reduction followed by nanoparticle formation is further augmented by the protein, as it also acts as a coating agent. The initial interaction of Hg 2+ with apo-a-LA was demonstrated by changes observed in absorption, emission, and CD spectroscopy, where the latter technique also detected structural changes in the protein. Such structural changes are expected when Hg 2+ binds to the protein, and therefore, the binding was determined by isothermal titration calorimetry (ITC). The binding was further proven by MALDI, which showed mercurated species of protein with a Gaussian distribution exhibiting a weighted average of 6 and 9 Hg 2+ ions bound to protein when apo-a-LA was treated with 10 and 100 equivalents, respectively. The molecular dynamics studies revealed the binding of Hg 2+ ions followed by the structural changes that occurred in the protein. The reaction between Hg 2+ and apo-a-LA yields noncrystalline nanoparticles at lower molar ratios of Hg 2+ and crystalline ones at higher molar ratios. The existence of both of these nanoparticles was proven by extensive TEM studies, and the mercury nanocrystals were further studied using fluorescence microscopy. X-ray photoelectron spectroscopy demonstrated that the protein has the ability to convert Hg 2+ to Hg 0 , and the resultant Hg 0 cluster is known to be less harmful than Hg 2+ to the organism. All of these studies support the use of apo-a-LA in the form of nanoparticles and nanocrystals to detoxify Hg 2+ .

Difunctional biogenic Au nanoparticles for colorimetric detection and removal of Hg2+

“…Since the previous report showed free thiols in amino acid sidechain (such as cysteine) could convert Hg 2+ to Hg 0 , We determined whether the colloid AuNPs contained proteins or peptides by Bradford method. 16 This result showed protein/peptide existed in the system with a This journal is © The Royal Society of Chemistry 2015 concentration about 11.4 mg mL À1 , which might mediate the Hg 2+ reduction. The existence of proteins/peptides capping in the surface of AuNPs was also conrmed by FTIR studies (Fig.…”