The transient production of anti-TNF-α antibody Adalimumab and a comparison of its characterization to the biosimilar Cinorra

Recombinant antibodies have emerged over the last few decades as the fastest growing class of therapeutic proteins for autoimmune diseases. Post-translation modifications of antibodies produced by human cell lines are highly consistent with those existing in natural human proteins and this is a major advantage of utilizing these cell lines. Cinorra is a biosimilar form of the antibody Adalimumab, which is an antagonist of TNF-α used for the treatment of autoimmune diseases. Adalimumab and Cinorra were produced by stable expression from CHO cells. The aim of this study was to select HEK cells as a host for producing Adalimumab to reveal whether the antibody produced by this human-derived cell line has similar characterization to Cinorra. Adalimumab was transiently produced in HEK-293T cells, characterized and analyzed for its properties. Circular dichroism spectroscopy confirmed a strong structural similarity of the expressed antibody with Cinorra. Likewise its binding activity and kinetic affinity to TNF-α (EC₅₀ = 416.5 ng/ml, KD = 3.89 E-10 M,) were highly similar to that of Cinorra (EC₅₀ = 421.2 ng/ml and KD = 3.34 E-10 M,). Additionally there was near identical neutralization of TNF-α-mediated cellular cytotoxicity (IC₅₀ of the expressed = 4.93 nM; IC₅₀ of Cinorra = 4.5 nM). Results indicate that Adalimumab produced by HEK-293T cells possesses a similarly efficient function and biological activity to Cinorra. Consequently, human-derived host cells with human post-translational modifications might potentially provide a basis for the development of Adalimumab with pharmaceutical properties for research and therapeutic use.

Folding and self-assembly of the TatA translocation pore based on a charge zipper mechanism

We propose a concept for the folding and self-assembly of the pore-forming TatA complex from the Twin-arginine translocase and of other membrane proteins based on electrostatic "charge zippers." Each subunit of TatA consists of a transmembrane segment, an amphiphilic helix (APH), and a C-terminal densely charged region (DCR). The sequence of charges in the DCR is complementary to the charge pattern on the APH, suggesting that the protein can be "zipped up" by a ladder of seven salt bridges. The length of the resulting hairpin matches the lipid bilayer thickness, hence a transmembrane pore could self-assemble via intra- and intermolecular salt bridges. The steric feasibility was rationalized by molecular dynamics simulations, and experimental evidence was obtained by monitoring the monomer-oligomer equilibrium of specific charge mutants. Similar "charge zippers" are proposed for other membrane-associated proteins, e.g., the biofilm-inducing peptide TisB, the human antimicrobial peptide dermcidin, and the pestiviral E(RNS) protein.

Magnetically oriented dodecylphosphocholine bicelles for solid-state NMR structure analysis

A mixture of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) with the short-chain detergent n-dodecylphosphocholine (DPC) is introduced here as a new membrane-mimetic bicelle system for solid-state NMR structure analysis of membrane proteins in oriented samples. Magnetically aligned DMPC/DPC bicelles are stable over a range of concentrations, with an optimum lipid ratio of q=3:1, and they can be flipped with lanthanide ions. The advantage of DMPC/DPC over established bicelle systems lies in the possibility to use one and the same detergent for purification and NMR analysis of the membrane protein, without any need for detergent exchange. Furthermore, the same batch of protein can be studied in both micelles and bicelles, using liquid-state and solid-state NMR, respectively. The applicability of the DMPC/DPC bicelles is demonstrated here with the (15)N-labeled transmembrane protein TatA.

Structure analysis of the protein translocating channel TatA in membranes using a multi-construct approach

The twin-arginine-translocase (Tat) can transport proteins in their folded state across bacterial or thylakoid membranes. In Bacillus subtilis the Tat-machinery consists of only two integral (inner) membrane proteins, TatA and TatC. Multiple copies of TatA are supposed to form the transmembrane channel, but little structural data is available on this 70-residue component. We used a multi-construct approach for expressing several characteristic fragments of TatA(d), to determine their individual structures and to cross-validate them comprehensively within the architecture of the full-length protein. Here, we report the design, high-yield expression, detergent-aided purification and lipid-reconstitution of five constructs of TatA(d), overcoming difficulties associated with the very different hydrophobicities and sizes of these membrane protein fragments. Circular dichroism (CD) and oriented CD (OCD) were used to determine their respective conformations and alignments in suitable, negatively charged phospholipid bilayers. CD spectroscopy showed an N-terminal alpha-helix, a central helical stretch, and an unstructured C-terminus, thus proving the existence of these secondary structures in TatA(d) for the first time. The OCD spectra demonstrated a transmembrane orientation of the N-terminal alpha-helix and a surface alignment of the central amphiphilic helix in lipid bilayers, thus supporting the postulated topology model and function of TatA as a transmembrane channel.