Binding of Apo and Glycated Human Serum Albumins to an Albumin-Selective Aptamer-Bound Graphene Quantum Dot Complex

Abstract

Diabetes mellitus is a chronic metabolic disease involving continued elevated blood glucose levels. It is a leading cause of mortality and reduced life expectancy. Glycated human serum albumin (GHSA) has been reported to be a potential diabetes biomarker. A nanomaterial-based aptasensor is one of the effective techniques to detect GHSA. Graphene quantum dots (GQDs) have been widely used in aptasensors as an aptamer fluorescence quencher due to their high biocompatibility and sensitivity. GHSA-selective fluorescent aptamers are first quenched upon binding to GQDs. The presence of albumin targets results in the release of aptamers to albumin and consequently fluorescence recovery. To date, the molecular details on how GQDs interact with GHSA-selective aptamers and albumin remain limited, especially the interactions of an aptamer-bound GQD (GQDA) with an albumin. Thus, in this work, molecular dynamics simulations were used to reveal the binding mechanism of human serum albumin (HSA) and GHSA to GQDA. The results show the rapid and spontaneous assembly of albumin and GQDA. Multiple sites of albumins can accommodate both aptamers and GQDs. This suggests that the saturation of aptamers on GQDs is required for accurate albumin detection. Guanine and thymine are keys for albumin-aptamer clustering. GHSA gets denatured more than HSA. The presence of bound GQDA on GHSA widens the entrance of drug site I, resulting in the release of open-chain glucose. The insight obtained here will serve as a base for accurate GQD-based aptasensor design and development.

Aggregation of Apo/Glycated Human Serum Albumins and Aptamer-Saturated Graphene Quantum Dot: A Simulation Study

“…During albumin–GQDA binding, the degrees of structural denaturation are computed in Table . Similar to the previous work, the adsorption of GQDA impairs the albumin structure. Glycated albumin (GHSA) shows lower helicity than ligand-free albumin (HSA).…”

“…This finding has also been seen in the previous GHSA studies. 40,43,48 Measuring this sugar release may thus be important for future GHSA detection design. The in-depth interaction analysis is explained later in the text.…”

“…Recently, the binding mechanism of GHSA to an aptamer-bound GQD complex has been studied, and no aptamer desorption was found. 43 This work also suggests that the saturation of the aptamer on GQD is required for accurate detection.…”

“…48−51 This impairment also alters the binding mechanisms of the albumin to the graphene sheet. 40,43 Molecular dynamics (MD) simulations have been successfully used to reveal the structural and functional properties of the albumins, 49,52−54 including their bindings to nanomaterials such as graphene, graphene oxide, and GQD. 55−58 Although the aggregation of the albumin with the aptamer-bound GQD was studied in order to understand the mechanism inside a diabetes aptasensor, 43 no mechanistic data about the assembly of GHSA and HSA with aptamer-saturated GQD is available yet.…”

“…Molecular dynamics (MD) simulations have been successfully used to reveal the structural and functional properties of the albumins, ,− including their bindings to nanomaterials such as graphene, graphene oxide, and GQD. − Although the aggregation of the albumin with the aptamer-bound GQD was studied in order to understand the mechanism inside a diabetes aptasensor, no mechanistic data about the assembly of GHSA and HSA with aptamer-saturated GQD is available yet. To this end, MD simulations were employed in this work to explore how both HSA and GHSA respond to the aptamer-saturated GQD in molecular detail.…”