Refolding of lysozyme by quasistatic and direct dilution reaction paths: a first-order-like state transition

Local ablation of gastric cancer by reconstituted apolipoprotein B lipoparticles carrying epigenetic drugs

Epigenetic inhibitors have shown anticancer effects. Combination chemotherapy with epigenetic inhibitors has shown high effectiveness in gastric cancer clinical trials, but severe side effect and local progression are the causes of treatment failure. Therefore, we sought to develop an acidity-sensitive drug delivery system to release drugs locally to diminish unfavorable outcome of gastric cancer. In this study, we showed that, as compared with single agents, combination treatment with the demethylating agent 5'-aza-2'-deoxycytidine and HDAC inhibitors Trichostatin A or LBH589 decreased cell survival, blocked cell cycle by reducing number of S-phase cells and expression of cyclins, increased cell apoptosis by inducing expression of Bim and cleaved Caspase 3, and reexpressed tumor suppressor genes more effectively in MGCC3I cells. As a carrier, reconstituted apolipoprotein B lipoparticles (rABLs) could release drugs in acidic environments. Orally administrated embedded drugs not only showed inhibitory effects on gastric tumor growth in a syngeneic orthotopic mouse model, but also reduced the hepatic and renal toxicity. In conclusion, we have established rABL-based nanoparticles embedded epigenetic inhibitors for local treatment of gastric cancer, which have good therapeutic effects but do not cause severe side effects.

Synthesis of apolipoprotein B lipoparticles to deliver hydrophobic/amphiphilic materials

To develop a drug delivery system (DDS), it is critical to address challenging tasks such as the delivery of hydrophobic and amphiphilic compounds, cell uptake, and the metabolic fate of the drug delivery carrier. Low-density lipoprotein (LDL) has been acknowledged as the human serum transporter of natively abundant lipoparticles such as cholesterol, triacylglycerides, and lipids. Apolipoprotein B (apo B) is the only protein contained in LDL, and possesses a binding moiety for the LDL receptor that can be internalized and degraded naturally by the cell. Therefore, synthetic/reconstituting apoB lipoparticle (rABL) could be an excellent delivery carrier for hydrophobic or amphiphilic materials. Here, we synthesized rABL in vitro, using full-length apoB through a five-step solvent exchange method, and addressed its potential as a DDS. Our rABL exhibited good biocompatibility when evaluated with cytotoxicity and cell metabolic response assays, and was stable during storage in phosphate-buffered saline at 4 °C for several months. Furthermore, hydrophobic superparamagnetic iron oxide nanoparticles (SPIONPs) and the anticancer drug M4N (tetra-O-methyl nordihydroguaiaretic acid), used as an imaging enhancer and lipophilic drug model, respectively, were incorporated into the rABL, leading to the formation of SPIONPs- and M4N- containing rABL (SPIO@rABL and M4N@rABL, respectively). Fourier transform infrared spectroscopy suggested that rABL has a similar composition to that of LDL, and successfully incorporated SPIONPs or M4N. SPIO@rABL presented significant hepatic contrast enhancement in T2-weighted magnetic resonance imaging in BALB/c mice, suggesting its potential application as a medical imaging contrast agent. M4N@rABL could reduce the viability of the cancer cell line A549. Interestingly, we developed solution-phase high-resolution transmission electron microscopy to observe both LDL and SPIO@rABL in the liquid state. In summary, our LDL-based DDS, rABL, has significant potential as a novel DDS for hydrophobic and amphiphilic materials, with good cell internalization properties and metabolicity.

Collapse kinetics of vibrated granular chains

The kinetics of the collapse of the coil state into condensed states is studied with vibrated granular chain composed of N metal beads partially immersed in water. The radius of gyration of the chain, R(g) is measured. For short chains (N < 140), disk-like condensed state is formed and R(g) decreases with time such that the function ΔR(g)(2) (≡ R(g)(2) - R(g)(2)(∞)) = A e(-t/τ), where the relaxation time τ follows a power-law dependence on the chain length N with an exponent γ = 1.9 ± 0.2. For the chains with length N ≥ 300, rod-like clusters are observed during the initial stage of collapse and R(g)(2) = R(g)(2)(0) - Bt(β), with β = 0.6 ± 0.1. In the coarsening stage, the exponential dependence of ΔR(g)(2) on time still holds, however, the relaxation time τ fluctuates and has no simple dependence on N. Furthermore, the time dependence of the averaged radius of gyration of the individual clusters, R(g,cl) can be described by the theory of Lifshitz and Slyozov. A peak in the structure function of long chains is observed in the initial stage of the collapse transition. The collapse transition in the bead chains is a first order phase transition. However, features of the spinodal decomposition are also observed.

FOLDING AND STRUCTURAL CHARACTERIZATION OF RECOMBINANT CYCLIN-DEPENDENT KINASE INHIBITOR p21(Cip1, Waf1, Sdi1)

p21Cip1, Waf1, Sdi1 (p21) is a member of the cyclin-dependent kinase (CDK) family of inhibitors in eukaryotes. We report the refolding of an inclusion body of a recombinant p21 (rp21) to its native form, under an alkaline to neutral environment, via an over-critical process describable by a first-order state transition model. The secondary structure of the refolded rp21 possesses a helical-major structure as determined by circular dichroism (CD) analysis, and its diameter is around 3 nm, as measured by dynamic light scattering studies (DLS) and atomic force microscopy (AFM). The differential scanning calorimeter (DSC) measurement indicates that the folded rp21 possesses unique but weak tertiary interactions. That the function of rp21 is reinstated upon refolding under our experimental conditions is evidenced by its binding to proliferating cell nuclear antigen (PCNA) in an immuno-co-precitptation analysis. The conformational changes of the folding intermediates of rp21 are consistent with the framework of a sequential model proposed earlier. The lack of a definitive structure of p21 in acidic condition will be discussed.

Direct observation of conformational folding coupled with disulphide rearrangement by using a water-soluble selenoxide reagent--a case of oxidative regeneration of ribonuclease A under weakly basic conditions

Oxidative regeneration pathways of bovine pancreatic ribonuclease A (RNase A), which has four SS linkages, were studied at 25 degrees C and pH 8.0 by using trans-3,4-dihydroxy-1-selenolane oxide (DHS(ox)), a new selenoxide reagent with strong oxidation power. The short-term folding study using a quench-flow instrument ( approximately 1 min) revealed that early intermediates (1S, 2S, 3S and 4S) are formed stochastically and irreversibly from the reduced protein (R) and do not have any stable structures. In the long-term folding study ( approximately 300 min), on the other hand, slow generation of the key intermediates (des[65-72] and des[40-95]) through SS rearrangement from the 3S intermediate ensemble was observed, followed by slight formation of native RNase A (N). The parallel UV and CD measurements demonstrated that formation of the key intermediates is accompanied with the formation of the native-like structures. Thus, DHS(ox) allowed facile identification of the conformational folding steps coupled with SS rearrangement on the major oxidative folding pathways.

Effect of sample loop dimension on lysozyme refolding in size-exclusion chromatography

The formation of misfolded protein aggregates, in particular inclusion bodies, has been widely considered as the major hindrance of good yield in refolding processes. To enhance the performance of protein refolding, extensive efforts were directed toward seeking out methods or means to reduce the aggregate production during the refolding process. Since simultaneous refolding and separation can be feasibly achieved within the packing matrices, size-exclusion chromatography (SEC) has been regarded as an efficient buffer exchange method to enhance protein refolding performance As of now, the effect of the process or operating parameters has yet to be thoroughly investigated. The present work is aimed at understanding how aggregate formation, as well as renaturation yield, varied with the diameter or length of sample loop in size-exclusion chromatography refolding process. Our results showed that not much difference was found in the patterns of aggregate formation for the contraction and the control cases. However, the formation of an additional peak was observed in the expansion cases. In addition, the amount of aggregates was not dependent on the sample loop diameter or length, but instead, influenced by injection volume and protein concentration. It was further concluded that a sample with large volume and low concentration was preferable for refolding process. We believe that the outcome from this work may shed light on the development of a more effective strategy for refolding processes.

Collective Dynamics of Lysozyme in Water: Terahertz Absorption Spectroscopy and Comparison with Theory

To directly measure the low-frequency vibrational modes of proteins in biologically relevant water environment rather than previously explored dry or slightly hydrated phase, we have developed a broadband terahertz spectrometer suitable for strongly attenuating protein solutions. Radiation is provided by harmonic multipliers (up to 0.21 THz), a Gunn oscillator (at 0.139 THz), and the UCSB free-electron lasers (up to 4.8 THz). Our spectrometer combines these intense sources with a sensitive cryogenic detector and a variable path length sample cell to detect radiation after it is attenuated by more than 7 orders of magnitudes by the aqueous sample. Using this spectrometer, we have measured the molar extinction of solvated lysozyme between 0.075 and 3.72 THz (2.5-124 cm(-1)), and we made direct comparison to several published theoretical models based on molecular dynamics simulations and normal-mode analysis. We confirm the existence of dense, overlapping normal modes in the terahertz frequency range. Our observed spectrum, while in rough qualitative agreement with these models, differs in detail. Further, we observe a low-frequency cutoff in terahertz dynamics between 0.2 and 0.3 THz, and we see no evidence of a predicted normal mode at approximately 0.09 THz for the protein.

Protein folding stabilizing time measurement: A direct folding process and three-dimensional random walk simulation

Protein particles undergo Brownian motion and collisions in solution. The diffusive collisions may lead to aggregation. For proteins to fold successfully the process has to occur quickly and before significant collision takes place. The speed of protein folding was deduced by studying the correlation time of a lysozyme refolding process from autocorrelation function analysis of the mean collision time and aggregation/soluble ratio of protein. It is a measure of time before which an aggregate can be formed and also is the time measure for a protein to fold into a stable state. We report on the protein folding stabilizing time of a lysozyme system to be 25.5-27.5 micros (<+/-4%) between 295 and 279K via direct folding experimental studies, supported by a three-dimensional random walk simulation of diffusion-limited aggregation model. Aggregation is suppressed when the protein is folded to a stable form. Spontaneous folding and diffusion-limited aggregation are antagonistic in nature. Meanwhile, the resultant aggresome, suggested by Raman and mass spectroscopy, may be formed by cross-linkages of disulfide bonds and hydrophobic interactions.