Engineering Protein–Gold Nanoparticle/Nanorod Complexation via Surface Modification for Protein Immobilization and Potential Therapeutic Applications

Abstract

Gold nanoparticles (AuNPs) and nanorods (AuNRs) find broad applications due to their unique optical and chemical properties. In biological applications, the contact of AuNPs/AuNRs with proteins is inevitable, resulting in the formation of a "protein corona", protein−particle agglomerates, or particle precipitation. While nonspecific adsorption or particle precipitation should be avoided, controllable protein adsorption and agglomerate formation via surface modification find applications in protein immobilization and therapeutics. Therefore, it becomes essential to understand the influences of particle surfaces on protein adsorption. Recently, we found a "problematic" globular protein, T4 lysozyme (T4L), precipitating AuNPs [Neupane et al. J. Phys. Chem. C. 2017, 121, 1377−1386. Herein, we systematically investigated the effects of surface modification on the adsorption of T4L. We found that both positively charged and neutral polymer coatings are effective in preventing such precipitation. In addition, for AuNPs with negative coatings, T4L could form either a stable protein corona or agglomerates, depending on the coating. For T4L and negatively coated AuNRs, only coronas were formed regardless of coating thickness. In all cases, we utilized EPR to detect protein rotational tumbling and backbone dynamics, which revealed the local environment that T4L experiences in these complexes. Such information is important for guiding future designs of gold nanomaterial−protein complexes with desired functions. Our findings demonstrate the importance of coatings on AuNP/AuNR functions in biological environments. With negative coatings, AuNPs/AuNRs can serve as immobilizers for carrying positively charged proteins. Furthermore, with proper coatings, a "precipitation-causing" protein could facilitate the formation of AuNP-based agglomerates which can have thermotherapeutic applications.

How Do Enzymes Orient When Trapped on Metal–Organic Framework (MOF) Surfaces?

“…Lysozyme activity test was done by monitoring the optical density of bacterial cell wall at 450 nm (OD450). 42 Upon confirming no change in OD450 was caused by ZIF-8 alone (Figure S1), we observed a substantial decay of OD450 (Figure 2D red dots) from hL/ZIF-8. The decay rate is slower than that of hL in buffer (Figure 2D black squares) under the same conditions, indicating hL trapped on ZIF-8 is only partially active.…”

“…Lysozyme activity test was done by monitoring the optical density of bacterial cell wall at 450 nm (OD450) . Upon confirming no change in OD450 was caused by ZIF-8 alone (Figure S1), we observed a substantial decay of OD450 (Figure D red dots) from hL/ZIF-8.…”

“…In SDSL, a protein site of interest is mutated to a cysteine, followed by attaching a stable nitroxyl moiety to form a spin label side chain (often known as “R1”) . Then, EPR’s “penetrating” power reports only the dynamics of the R1 side chain, regardless of the interferences from the background materials. ,− SDSL-EPR has been applied to probe structural information on proteins adsorbed to solid surfaces or porous materials. − For cysteine-rich proteins, unnatural amino acids can be used to attach the spin label side chain . In this work, for proof-of-principle, we determined the orientation of a model enzyme, lysozyme, trapped on the surface of ZIF-8 using SDSL-EPR.…”

Probing the Mechanism of Antibody-Triggered Aggregation of Gold Nanoparticles

“…Several mechanisms have been proposed for protein-induced nanoparticle aggregation. ,,− For some proteins, aggregation of AuNPs is ascribed to the unfolding of protein upon adsorption followed by destabilization of the conjugate. , Zhang et al first reported that lyzosyme undergoes a conformational change upon adsorption to AuNPs at physiological pH and that the partially unfolded protein promotes the formation of large amorphous protein–AuNP aggregates . Similarly, it was reported that, at low concentrations, BSA unfolds upon adsorption to gold nanorods and induces aggregation .…”

Facile Synthesis of Peptide-Conjugated Gold Nanoclusters with Different Lengths

“…Considering the much larger size of peptides compared with the nanoclusters, the synthesis of peptide-coated nanoclusters may be complex. Moreover, many protein-conjugated Au NSs have been prepared with more diverse and powerful applications [8,[34][35][36][37][38], which are typically directly immobilized by non-specific interactions [39,40]. Here, the conjugation of a lengthy peptide on Au NSs can be the first step toward site-specific protein modification.…”