Selectivity and Resolving Power of Hydrophobic Interaction Chromatography Targeting the Separation of Monoclonal Antibody Variants.

This study presents a comprehensive investigation of the mechanistic understanding of retention and selectivity in hydrophobic interaction chromatography. It provides valuable insights into crucial method-development parameters involved in achieving chromatographic resolution for profiling molecular variants of trastuzumab. Retention characteristics have been assessed for three column chemistries, i.e., butyl, alkylamide, and long-stranded multialkylamide ligands, while distinguishing column hydrophobicity and surface area. Salt type and specifically chloride ions proved to be the key driver for improving chromatographic selectivity, and this was attributed to the spatial distribution of ions at the protein surface, which is ion-specific. The effect was notably more pronounced on the multialkylamide column, as proteins intercalated between the multiamide polymer strands, enabling steric effects. Column coupling proved to be an effective approach for maximizing resolution between molecular variants present in the trastuzumab reference sample and trastuzumab variants induced by forced oxidation. Liquid chromatography-mass spectrometry (LC-MS)/MS peptide mapping experiments after fraction collection indicate that the presence of chloride in the mobile phase enables the selectivity of site-specific deamidation (N30) situated at the heavy chain. Moreover, site-specific oxidation of peptides (M255, W420, and M431) was observed for peptides situated at the Fc region close to the CH2-CH3 interface, previously reported to activate unfolding of trastuzumab, increasing the accessible surface area and hence resulting in an increase in chromatographic retention.

Legumain Functions as a Transient TrkB Sheddase.

While primarily found in endo-lysosomal compartments, the cysteine protease legumain can also translocate to the cell surface if stabilized by the interaction with the RGD-dependent integrin receptor αVß3. Previously, it has been shown that legumain expression is inversely related to BDNF-TrkB activity. Here we show that legumain can conversely act on TrkB-BDNF by processing the C-terminal linker region of the TrkB ectodomain in vitro. Importantly, when in complex with BDNF, TrkB was not cleaved by legumain. Legumain-processed TrkB was still able to bind BDNF, suggesting a potential scavenger function of soluble TrkB towards BDNF. The work thus presents another mechanistic link explaining the reciprocal TrkB signaling and δ-secretase activity of legumain, with relevance for neurodegeneration.

At-line quantitative profiling of monoclonal antibody products during bioprocessing using HPLC-MS.

(1) Background: The N-glycosylation profile as well as the subunit assembly of monoclonal antibodies (mAbs) are strongly dependent on manufacturing conditions and thus need to be monitored during the bioprocess. Commonly, mAbs are characterized downstream of the fermentation process applying different analytical techniques like released glycan analysis, peptide mapping, or subunit profiling. However, these procedures are time-consuming and difficult to perform in real-time. (2) Methods: We applied a simple HPLC-MS workflow with minimal sample preparation to characterize mAb product quality at the intact protein level at different time points during fermentation. After harvest, the cell culture medium was centrifuged briefly. The supernatant containing the fermentation product was diluted and immediately subjected to HPLC-MS analysis. (3) Results: Besides the product of interest (mAb), the fermentation broth contained misassembled variants, mostly light chain and light chain dimer. The mAb's glycosylation profile changed over time showing an increase in galactosylated variants with G0F/G1F being the most abundant glycoform at all time points of fermentation. Furthermore, expressed protein species were relatively and absolutely quantified. The workflow was very robust despite analyzing a highly complex matrix. Relative standard deviations for retention times were below 0.5% for both intra and inter-day comparison, whereas relative procedural standard deviations for quantification of the different protein species ranged between 7 and 13%. (4) Conclusions: This approach allows for reliable analysis of product profiles of monoclonal antibody species including misassembled subunits and glycosylation variants directly from fermentation broth using a fast and robust HPLC-MS workflow.

Biotyping of IRE/CTVM19 tick cell line infected by tick-borne encephalitis virus.

Ticks, being vectors for a variety of pathogens such as tick-borne encephalitis virus (TBEV), have developed defense mechanisms and pathways against infections, allowing them to control the virus at a level that does not hinder their fitness and development. At the present moment, only a few studies focused on interactions between ticks and TBEV on a molecular level have been published. Here, a possible application of MALDI-TOF MS as a research tool for the investigation of tick-virus interactions was shown. Mass spectrometry (MS) profiles of TBEV-infected and non-infected IRE/CTVM19 tick cell line were compared using principal component analysis. MS spectra were clustered based on the cultivation time of cells, but not their infection status. Nevertheless, the analysis of loading plots revealed different factors (peaks) being involved in the clustering of infected and non-infected cells. Out of them, nine were assigned with proteins: five and four for non-infected and infected cells, respectively. Peak with m/z 8565 was found to be of interest because it was suppressed upon TBEV infection and assigned to proteasome subunit alpha type (B7QE67).

Development, characterization, and application of a 2-Compartment system to investigate the impact of pH inhomogeneities in large-scale CHO-based processes.

Large-scale bioreactors for the production of monoclonal antibodies reach volumes of up to 25 000 L. With increasing bioreactor size, mixing is however affected negatively, resulting in the formation of gradients throughout the reactor. These gradients can adversely affect process performance at large scale. Since mammalian cells are sensitive to changes in pH, this study investigated the effects of pH gradients on process performance. A 2-Compartment System was established for this purpose to expose only a fraction of the cell population to pH excursions and thereby mimicking a large-scale bioreactor. Cells were exposed to repeated pH amplitudes of 0.4 units (pH 7.3), which resulted in decreased viable cell counts, as well as the inhibition of the lactate metabolic shift. These effects were furthermore accompanied by increased absolute lactate levels. Continuous assessment of molecular attributes of the expressed target protein revealed that subunit assembly or N-glycosylation patterns were only slightly influenced by the pH excursions. The exposure of more cells to the same pH amplitudes further impaired process performance, indicating this is an important factor, which influences the impact of pH inhomogeneity. This knowledge can aid in the design of pH control strategies to minimize the effects of pH inhomogeneity in large-scale bioreactors.

Tissue-specific signatures in tick cell line MS profiles.

BACKGROUND: The availability of tick in vitro cell culture systems has facilitated many aspects of tick research, including proteomics. However, certain cell lines have shown a tissue-specific response to infection. Thus, a more thorough characterization of tick cell lines is necessary. Proteomic comparative studies of various tick cell lines will contribute to more efficient application of tick cell lines as model systems for investigation of host-vector-pathogen interactions. RESULTS: Three cell lines obtained from a hard tick, Ixodes ricinus, and two from I. scapularis were investigated. A cell mass spectrometry approach (MALDI-TOF MS) was applied, as well as classical proteomic workflows. Using PCA, tick cell line MS profiles were grouped into three clusters comprising IRE/CTVM19 and ISE18, IRE11 and IRE/CTVM20, and ISE6 cell lines. Two other approaches confirmed the results of PCA: in-solution digestion followed by nanoLC-ESI-Q-TOF MS/MS and 2D electrophoresis. The comparison of MS spectra of the cell lines and I. ricinus tick organs revealed 29 shared peaks. Of these, five were specific for ovaries, three each for gut and salivary glands, and one for Malpighian tubules. For the first time, characteristic peaks in MS profiles of tick cell lines were assigned to proteins identified in acidic extracts of corresponding cell lines. CONCLUSIONS: Several organ-specific MS signals were revealed in the profiles of tick cell lines.

Satellite DNA in Vicia faba is characterized by remarkable diversity in its sequence composition, association with centromeres, and replication timing.

Satellite DNA, a class of repetitive sequences forming long arrays of tandemly repeated units, represents substantial portions of many plant genomes yet remains poorly characterized due to various methodological obstacles. Here we show that the genome of the field bean (Vicia faba, 2n = 12), a long-established model for cytogenetic studies in plants, contains a diverse set of satellite repeats, most of which remained concealed until their present investigation. Using next-generation sequencing combined with novel bioinformatics tools, we reconstructed consensus sequences of 23 novel satellite repeats representing 0.008-2.700% of the genome and mapped their distribution on chromosomes. We found that in addition to typical satellites with monomers hundreds of nucleotides long, V. faba contains a large number of satellite repeats with unusually long monomers (687-2033 bp), which are predominantly localized in pericentromeric regions. Using chromatin immunoprecipitation with CenH3 antibody, we revealed an extraordinary diversity of centromeric satellites, consisting of seven repeats with chromosome-specific distribution. We also found that in spite of their different nucleotide sequences, all centromeric repeats are replicated during mid-S phase, while most other satellites are replicated in the first part of late S phase, followed by a single family of FokI repeats representing the latest replicating chromatin.