Interaction of nanoparticles with proteins: relation to bio-reactivity of the nanoparticle

Abstract

Interaction of nanoparticles with proteins is the basis of nanoparticle bio-reactivity. This interaction gives rise to the formation of a dynamic nanoparticle-protein corona. The protein corona may influence cellular uptake, inflammation, accumulation, degradation and clearance of the nanoparticles. Furthermore, the nanoparticle surface can induce conformational changes in adsorbed protein molecules which may affect the overall bio-reactivity of the nanoparticle. In depth understanding of such interactions can be directed towards generating bio-compatible nanomaterials with controlled surface characteristics in a biological environment. The main aim of this review is to summarise current knowledge on factors that influence nanoparticle-protein interactions and their implications on cellular uptake.

Figure 1

Schematic representation of NP surface induced unfolding of the interacting protein molecule and consequences. (A) Protein molecules adsorb on to the NP surface, to form a complex termed as the (B) NP-PC.NP surface may induce conformational change to the native structure of the adsorbed protein molecule, causing it to unfold. Such protein conformational changesmay either (C) alter the function of the native protein moleculeor even lead to (D) exposure of “cryptic” epitopes which may result in immunological recognition of the complex.

Figure 2

Interaction of nanoparticles with the cellular interface. NPs interact with cells via the protein corona. (A) Uptake of large sized NP-protein complexes, agglomerates of NP may be ingested by specialized cells such as macrophages and neutrophils via phagocytosis. It involves folding of the plasma membrane over the NP complex to form the phagosome. (B) Non-specific uptake of extracellular fluid containing aggregates of NP may also be taken up by cells via macropinocytosis which involves ruffling of the plasma membrane to form vesicles which ultimately fuse to form lysosomes. Endocytosis of NP complexes may also be directed by specific receptors involving formation of (C) caveolae that are plasma membrane indentations consisting of cholesterol binding proteins called caveolins or (D) clathrin-coated vesicles. (E) Apart from these other endocytic mechanisms, independent of clathrin or caveolae may also facilitate uptake of NP.

Figure 3

Schematic representation of the commonly used strategy to isolate and identify surface adsorbed proteins, when nanoparticles interact with complex protein mixtures. (A) Incubation of NP with protein solutions results in adsorption of protein onto the NP surface. Protein concentration may affect the amount and identity of proteins adsorbed on the presented NP surface. (B) Centrifugation for removal of unbound proteins followed by repeated washing of the NP-protein pellet is important for isolation of the “hard protein corona”. (C) Isolation of the NP-PC can be achieved by elution of the adsorbed proteins using denaturing agents such as Laemmli buffer which contains sodium dodecyl sulphate and 2-mercaptoethanol that facilitate the overall desorption of the proteins. (D) The desorbed proteins can thus be separated using one or two dimensional gel electrophoresis. (E) Separated protein bands of interest can further be subjected to tryptic digestion and can be subsequently identified using mass spectrometric methods.