Detection and characterization of large-scale protein conformational transitions in solution using charge-state distribution analysis in ESI-MS

Improvement of Certolizumab Fab' properties by PASylation technology

Certolizumab pegol is a Fab' antibody fragment for treatment of rheumatoid arthritis and Crohn's disease which is conjugated to a 40 kDa PEG molecule in order to increase the protein half-life. PEGylation may have disadvantages including immunogenicity, hypersensitivity, vacuolation, decreased binding affinity and biological activity of the protein. To overcome these problems, PASylation has been developed as a new approach. The nucleotide sequence encoding 400 amino acid PAS residues was genetically fused to the corresponding nucleotide sequences of both chains of certolizumab. Then, the bioactivity as well as physicochemical and pharmacokinetic properties of the recombinant PASylated expressed protein was assayed. Circular dichroism spectroscopy demonstrated that the random coil structure of PAS sequences did not change the secondary structure of the PASylated Fab' molecule. It was observed that PASylation influenced the properties of the Fab' molecule by which the hydrodynamic radius and neutralization activity were increased. Also, the antigen binding and binding kinetic parameters improved in comparison to the PEGylated Fab' antibody. Pharmacokinetic studies also showed prolonged terminal half-life and improved pharmacokinetic parameters in PASylated recombinant protein in comparison to the PEGylated and Fab' control molecules. The results reconfirmed the efficiency of PASylation approach as a potential alternative method in increasing the half-life of pharmaceutical proteins.

Exploring the Structural Diversity in Inhibitors of α-Synuclein Amyloidogenic Folding, Aggregation, and Neurotoxicity

Aggregation of α-Synuclein (αS) protein to amyloid fibrils is a neuropathological hallmark of Parkinson's disease (PD). Growing evidence suggests that extracellular αS aggregation plays a pivotal role in neurodegeneration found in PD in addition to the intracellular αS aggregates in Lewy bodies (LB). Here, we identified and compared a diverse set of molecules capable of mitigating protein aggregation and exogenous toxicity of αSA53T, a more aggregation-prone αS mutant found in familial PD. For the first time, we investigated the αS anti-amyloid activity of semi-synthetic flavonoid 2', 3', 4' trihydroxyflavone or 2-D08, which was compared with natural flavones myricetin and transilitin, as well as such structurally diverse polyphenols as honokiol and punicalagin. Additionally, two novel synthetic compounds with a dibenzyl imidazolidine scaffold, Compound 1 and Compound 2, were also investigated as they exhibited favorable binding with αSA53T. All seven compounds inhibited αSA53T aggregation as demonstrated by Thioflavin T fluorescence assays, with modified fibril morphology observed by transmission electron microscopy. Ion mobility-mass spectrometry (IM-MS) was used to monitor the structural conversion of native αSA53T into amyloidogenic conformations and all seven compounds preserved the native unfolded conformations of αSA53T following 48 h incubation. The presence of each test compound in a 1:2 molar ratio was also shown to inhibit the neurotoxicity of preincubated αSA53T using phaeochromocytoma (PC12) cell viability assays. Among the seven tested compounds 2-D08, honokiol, and the synthetic Compound 2 demonstrated the highest inhibition of aggregation, coupled with neuroprotection from preincubated αSA53T in vitro. Molecular docking predicted that all compounds bound near the lysine-rich region of the N-terminus of αSA53T, where the flavonoids and honokiol predominantly interacted with Lys 23. Overall, these findings highlight that (i) restricted vicinal trihydroxylation in the flavone B-ring is more effective in stabilizing the native αS conformations, thus blocking amyloidogenic aggregation, than dihydroxylation aggregation in both A and B-ring, and (ii) honokiol, punicalagin, and the synthetic imidazolidine Compound 2 also inhibit αS amyloidogenic aggregation by stabilizing its native conformations. This diverse set of molecules acting on a singular pathological target with predicted binding to αSA53T in the folding-prone N-terminal region may contribute toward novel drug-design for PD.

Mass spectrometry for the biophysical characterization of therapeutic monoclonal antibodies

Monoclonal antibodies (mAbs) are powerful therapeutics, and their characterization has drawn considerable attention and urgency. Unlike small-molecule drugs (150-600 Da) that have rigid structures, mAbs (∼150 kDa) are engineered proteins that undergo complicated folding and can exist in a number of low-energy structures, posing a challenge for traditional methods in structural biology. Mass spectrometry (MS)-based biophysical characterization approaches can provide structural information, bringing high sensitivity, fast turnaround, and small sample consumption. This review outlines various MS-based strategies for protein biophysical characterization and then reviews how these strategies provide structural information of mAbs at the protein level (intact or top-down approaches), peptide, and residue level (bottom-up approaches), affording information on higher order structure, aggregation, and the nature of antibody complexes.

Endosomolytic reducible polymeric electrolytes for cytosolic protein delivery

Despite the numerous vital functions of proteins in the cytosolic compartment, less attention has been paid to the delivery of protein drugs to the cytosol than to the plasma membrane. To address this issue and effectively deliver charged proteins into the cytoplasm, we used endosomolytic, thiol-triggered degradable polyelectrolytes as carriers. The cationic, reducible polyelectrolyte RPC-bPEI(0.8 kDa)2 was synthesized by the oxidative polymerization of thiolated branched polyethyleneimine (bPEI). The polymer was converted to the anionic, reducible polyelectrolyte RPA-bPEI(0.8 kDa)2 by introducing carboxylic acids. The two reducible polyelectrolytes (RPC-bPEI(0.8 kDa)2 and RPA-bPEI(0.8 kDa)2) were complexed with counter-charged model proteins (bovine serum albumin (BSA) and lysozyme (LYZ)), forming polyelectrolyte/protein complexes of less than 200 nm in size at weight ratios (WR) of ≥1. The resultant complexes maintained a proton buffering capacity nearly equivalent to that of the polyelectrolytes in the absence of protein complexation and were cytocompatible with MCF7 human breast carcinoma cells. Under cytosol-mimicking thiol-rich conditions, RPC-bPEI(0.8 kDa)2/BSA and RPA-bPEI(0.8 kDa)2/LYZ complexes increased significantly in size and released the loaded protein, unlike the protein complexes with nonreducible polyelectrolytes (bPEI(25 kDa) and bPEI(25 kDa)COOH). The polyelectrolyte/protein complexes showed cellular uptake similar to that of the corresponding proteins alone, but the former allowed more protein to escape into the cytosol from endolysosomes than the latter as a result of the endosomolytic function of the polyelectrolytes. In addition, the proteins in the polyelectrolyte/protein complexes kept their intrinsic secondary structures. In conclusion, the results show the potential of the designed endosomolytic, reducible polyelectrolytes for the delivery of proteins to the cytosol.