Investigation of the nanoparticle protein corona, the shell of plasma proteins formed around nanoparticles immediately after they enter the bloodstream, is a benchmark in the study of the applications of nanoparticles in all fields of medicine, from pharmacology to toxicology. We report the first investigation of the protein corona adsorbed onto single-walled carbon nanotubes modified with 2 kDa molecular weight polyethylene glycol chains [PEG(2k)-modified SWCNTs or PEG2-SWCNTs] by using a large-scale gel-based proteomics method on biological replicates. More than 240 plasma proteins were selected, and their differences were analyzed among PEG2-SWCNTs differing in surface charge and PEG conformation. The protein corona of PEG2-SWCNTs showed that coagulation proteins, immunoglobulins, apolipoproteins, and proteins of the complement system were among the proteins bound by PEG2-SWCNTs and that their recruitment was independent from the isoelectric point, molecular weight, total hydrophobicity, and number of polyaromatic residues of the proteins. Statistical analysis on protein relative abundance revealed that PEG conformation had a higher influence on the PEG2-SWCNTs' protein corona repertoire than nanotube surface charge. PEG conformation also affected the biological performance of PEG2-SWCNTs. A change in PEG conformation from mushroom to mushroom-brush transition affected the competitive adsorption of the major constituents of the protein corona of PEG2-SWCNTs and promoted shorter blood circulation time, faster renal excretion, and higher relative spleen versus liver uptake of PEG2-SWCNTs. Our data suggest that the protein corona, along with steric stabilization, may mediate the action of PEG conformation on the pharmacokinetic profile of PEG-modified SWCNTs.

Since their discovery at the end of the previous millennium, carbon nanotubes (CNTs) have been the object of thousands of papers describing their applications in fields ranging from physics to electronics, photonics, chemistry, biology, and medicine. The development of chemical approaches to modify their graphitic sidewalls enabled the generation of poly(ethylene glycol) (PEG)-modified CNTs and their exploration in multiple biomedical applications. Studies at the cellular and organism level revealed that PEG-modified CNTs have favorable pharmacokinetic and toxicology profiles. Recently, PEG-modified CNTs have been successfully tested in preclinical studies in the fields of oncology, neurology, vaccination, and imaging, suggesting that they are well suited for the generation of novel multifunctional nanodrugs. Here we will review published data about the application of PEG-modified CNTs as in vitro and in vivo therapeutic and imaging tools and describe what is known about the interaction between PEG-modified CNTs and biological systems. Although several pieces of the puzzle are still missing, we will also attempt to formulate a preliminary structure-function model for PEG-modified CNT cellular trafficking, disposition, and side effects.

Presteady-state and steady-state kinetic studies performed on human glutathione transferase P1-1 (EC 2.5.1.18) with 1-chloro-2,4-dinitrobenzene as co-substrate indicate that the rate-determining step is a physical event that occurs after binding of the two substrates and before the -complex formation. It may be a structural transition involving the ternary complex. This event can be related to diffusion-controlled motions of protein portions as k cat°/ k cat linearly increases by raising the relative viscosity of the solution. Similar viscosity dependence has been observed for K m GSH , while K m CDNB is independent. No change of the enzyme structure by viscosogen has been found by circular dichroism analysis. Thus, k cat and K m GSH seem to be related to the frequency and extent of enzyme structural motions modulated by viscosity. Interestingly, the reactivity of Cys-47 which can act as a probe for the flexibility of helix 2 is also modulated by viscosity. Its viscosity dependence parallels that observed for k cat and K m GSH , thereby suggesting a possible correlation between k cat , K m GSH, and diffusioncontrolled motion of helix 2. The viscosity effect on the kinetic parameters of C47S and C47S/C101S mutants confirms the involvement of helix 2 motions in the modulation of K m GSH, whereas a similar role on k cat cannot be ascertained unequivocally. The flexibility of helix 2 modulates also the homotropic behavior of GSH in these mutants. Furthermore, fluorescence experiments support a structural motion of about 4 Å occurring between helix 2 and helix 4 when GSH binds to the G-site.Human placental glutathione transferase P1-1 (GST) 1 (EC 2.5.1.18) is a dimeric enzyme composed of two identical subunits each containing one binding site for GSH (G-site) and a second binding site for the electrophilic co-substrate (H-site). Inspection of the three-dimensional structure indicates the presence near the G-site of the irregular ␣ helix 2 (residues 37-46) which is exposed to the solvent (1). Lys-44, a part of this helix, is involved in the binding of GSH. At the end of helix 2 is Cys-47 which is probably linked by ion pair formation with Lys-54. This electrostatic interaction seems important for the correct spatial arrangement of the G-site (2); lack of this bond by replacement of Cys-47 or Lys-54 with Ser or Ala lowers the affinity for GSH and triggers a positive cooperativity toward the binding of GSH (3, 4). We therefore suggested that Cys-47 acts as a hinge which limits the extent or frequency of conformational transitions involving helix 2 (3, 4). In its absence, helix 2 would become more flexible and contact the adjacent subunit via helix 4 thereby inducing the observed cooperativity (4). Several pieces of evidence indicate that the irregular ␣ helix 2 is a flexible region even in the wild-type enzyme; it displays the highest temperature factors among all other regions of domain I (5); moreover, it offers the sole point of attack (Lys-44) for the proteolytic cleavage by trypsin (5). Finally, the strongest evide...

Why are there so many dimeric proteins and enzymes? While for heterodimers a functional explanation seems quite reasonable, the case of homodimers is more puzzling. The number of homodimers found in all living organisms is rapidly increasing. A thorough inspection of the structural data from the available literature and stability (measured from denaturation–renaturation experiments) allows one to suggest that homodimers can be divided into three main types according to their mass and the presence of a (relatively) stable monomeric intermediate in the folding–unfolding pathway. Among other explanations, we propose that an essential advantage for a protein being dimeric may be the proper and rapid assembly in the cellular milieu.

Osteoarthritis (OA) is a common and debilitating degenerative disease of articular joints for which no disease-modifying medical therapy is currently available. Inefficient delivery of pharmacologic agents into cartilage-resident chondrocytes after systemic administration has been a limitation to the development of anti-OA medications. Direct intra-articular injection enables delivery of high concentrations of agents in close proximity to chondrocytes; however, the efficacy of this approach is limited by the fast clearance of small molecules and biomacromolecules after injection into the synovial cavity. Coupling of pharmacologic agents with drug delivery systems able to enhance their residence time and cartilage penetration can enhance the effectiveness of intra-articularly injected anti-OA medications. Herein we describe an efficient intra-articular delivery nanosystem based on single-walled carbon nanotubes (SWCNTs) modified with polyethylene glycol (PEG) chains (PEG-SWCNTs). We show that PEG-SWCNTs are capable to persist in the joint cavity for a prolonged time, enter the cartilage matrix, and deliver gene inhibitors into chondrocytes of both healthy and OA mice. PEG-SWCNT nanoparticles did not elicit systemic or local side effects. Our data suggest that PEG-SWCNTs represent a biocompatible and effective nanocarrier for intra-articular delivery of agents to chondrocytes.

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Two mutants of the blue copper protein azurin from Pseudomonas aeruginosa, Ile7Ser and Phe110Ser, were prepared. The mutations were aimed at affecting the mobility and the fluorescence properties of Trp48, the only tryptophan residue present, which in the wild-type protein is located in a highly hydrophobic and rigid environment. EPR, UV-vis, and NMR spectroscopy show that the copper binding site and the overall structure of the wild-type protein are preserved and that structural effects occur only on a local scale. Steady-state fluorescence spectra of both mutants, particularly in the copper-free form, show that tryptophan fluorescence is dramatically affected by the introduction of a polar residue close to it. The emission maximum is red-shifted and dependent on the excitation wavelength. This indicates a loosening of the matrix around the indolyl side chain and an increase of the effective dielectric constant of the microenvironment. Time-resolved fluorescence spectroscopy also shows substantial changes in the fluorescence lifetimes and in the distribution of the lifetimes of the mutants; these variations are interpreted in terms of a change in solvation of the Trp48 side chain.

We report the formation of a supramolecular luminescent nanoassembly composed of individual or small ropes of full-length, single-walled carbon nanotubes decorated with streptavidin-conjugated quantum dots. The supramolecular luminescent nanoassembly was stably dispersed under physiological conditions and was readily visible by both optical and confocal fluorescent microscopies. Jurkat T leukemia cells were able to internalize the nanoassembly by multivalent CD3 receptor-mediated endocytosis (adsorption by cell). Once internalized by cells, the nanoassembly was found to be transported to lysosomes. These properties should make this supramolecular luminescent nanoassembly an excellent building block for the construction of intracellular polyvalent nanoprobes, mimicking natural viral delivery entities with enhanced loading capacity compared to small molecules.