Insulin and Human Serum Albumin Interactions with Core–Shell Fe3O4@SiO2 Nanoparticles Functionalized with Carboranes

TL;DR

This study explores how specific nanoparticles interact with human serum albumin and insulin, causing structural changes that could impact their function in medical applications.

Contribution

The novelty lies in analyzing the enthalpy–entropy-driven interactions of functionalized Fe3O4@SiO2 nanoparticles with two specific proteins using multiple experimental techniques.

Findings

Human serum albumin (HSA) undergoes significant structural changes when interacting with nanoparticles, reducing its α-helix content from 87.59% to 40.9%.

Insulin shows weaker interaction with nanoparticles compared to HSA, with only a 15% decrease in α-structure content.

Nanoparticle exposure alters the microenvironment around tryptophan residues, increasing hydrophobicity for both proteins.

Abstract

In a biological medium,
nanoparticles (NPs) can spontaneously
interact
with proteins, adsorb onto their surface, and cause conformational
and orientation changes of the proteins. As a result, the protein
function is influenced in a complex manner. Therefore, a detailed
understanding of the nature and specificity of protein–nanoparticle
interactions is crucial for the application of functional NPs in medicine.
In the presented work, we studied the interactions of GMA-treated
SiO2 NPs with the Fe3O4 core and
attached carborane compounds (Fe3O4/TEOS/TMSPM/GMA/Carborane),
designed for boron neutron capture therapy, with human serum albumin
(HSA) and insulin. We combined different techniques: spectrofluorometry,
circular dichroism spectroscopy, and isothermal titration calorimetry
to address this issue. The results show that the adsorption of protein
onto the NP surface is enthalpy–entropy-driven, with ensuing
structural changes of the protein. As for albumin, the percentage
of the α-helix structure in the protein is significantly reduced
from 87.59 (free protein) to 40.9% for an NP concentration of 1.8
mg/mL, while the content of the β-sheet and random coil increases
from 0.48 to 8.78% and from 11.93 to 50.32%, respectively. The interaction
between NPs and small protein–insulin is weaker than that for
HSA, confirming less negative ΔH and a 15%
decrease in the α-structure content for the highest concentration
of NPs. For both proteins, the exposure on Fe3O4/TEOS/TMSPM/GMA/Carborane affects the polarity of the microenvironment
around Trp, which is consequently exposed to a more hydrophobic environment.
Calculated values of the radius of gyration and the minimum distance
between the proteins and the NPs indicate a stronger interaction and
closer binding proximity to the NPs, corroborating experimental observations
of the higher binding affinity of HSA to NPs.

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