Introduction of Carbonyl Groups into Antibodies

Antibodies and their derivatives (scFv, Fabs, etc.) represent a unique class of biomolecules that combine selectivity with the ability to target drug delivery. Currently, one of the most promising endeavors in this field is the development of molecular diagnostic tools and antibody-based therapeutic agents, including antibody-drug conjugates (ADCs). To meet this challenge, it is imperative to advance methods for modifying antibodies. A particularly promising strategy involves the introduction of carbonyl groups into the antibody that are amenable to further modification by biorthogonal reactions, namely aliphatic, aromatic, and α-oxo aldehydes, as well as aliphatic and aryl-alkyl ketones. In this review, we summarize the preparation methods and applications of site-specific antibody conjugates that are synthesized using this approach.

Comparison of Four Immobilization Methods for Different Transaminases

Biocatalytic syntheses often require unfavorable conditions, which can adversely affect enzyme stability. Consequently, improving the stability of biocatalysts is needed, and this is often achieved by immobilization. In this study, we aimed to compare the stability of soluble and immobilized transaminases from different species. A cysteine in a consensus sequence was converted to a single aldehyde by the formylglycine-generating enzyme for directed single-point attachment to amine beads. This immobilization was compared to cross-linked enzyme aggregates (CLEAs) and multipoint attachments to glutaraldehyde-functionalized amine- and epoxy-beads. Subsequently, the reactivity and stability (i.e., thermal, storage, and solvent stability) of all soluble and immobilized transaminases were analyzed and compared under different conditions. The effect of immobilization was highly dependent on the type of enzyme, the immobilization strategy, and the application itself, with no superior immobilization technique identified. Immobilization of HAGA-beads often resulted in the highest activities of up to 62 U/g beads, and amine beads were best for the hexameric transaminase from Luminiphilus syltensis. Furthermore, the immobilization of transaminases enabled its reusability for at least 10 cycles, while maintaining full or high activity. Upscaled kinetic resolutions (partially performed in a SpinChemTM reactor) resulted in a high conversion, maintained enantioselectivity, and high product yields, demonstrating their applicability.

Nanobodies: From Serendipitous Discovery of Heavy Chain-Only Antibodies in Camelids to a Wide Range of Useful Applications

The presence of unique heavy chain-only antibodies (HCAbs) in camelids was discovered at Vrije Universiteit Brussel (VUB, Brussels, Belgium) at a time when many researchers were exploring the cloning and expression of smaller antigen-binding fragments (Fv and Fab) from hybridoma-derived antibodies. The potential importance of this discovery was anticipated, and efforts were immediately undertaken to understand the emergence and ontogeny of these HCAbs as well as to investigate the applications of the single-domain antigen-binding variable domains of HCAbs (nanobodies). Nanobodies were demonstrated to possess multiple biochemical and biophysical advantages over other antigen-binding antibody fragments and alternative scaffolds. Today, nanobodies have a significant and growing impact on research, biotechnology, and medicine.

Cytoplasmic Expression of Nanobodies with Formylglycine Generating Enzyme Tag and Conversion to a Bio-Orthogonal Aldehyde Group

Nanobodies (Nbs) can be successfully retrieved following phage, bacterial, yeast, or ribosome display of immune, synthetic, or naïve libraries. However, after panning, multiple individual Nb clones need to be screened and assessed for solubility, antigen specificity, affinity, and potential biological function. Therefore, it is highly desirable to have a convenient expression strategy to obtain sufficient protein for in-depth characterization of the Nbs. The presence of a purification and detection tag, as well as a chemically reactive group to enable simple generation of Nb derivatives, would be of great help in this regard. Here, we provide a general protocol for high yield cytoplasmic expression and purification of formylglycine generating enzyme (FGE)-tagged Nbs. The cysteine within the FGE tag is easily converted to formylglycine by passing the FGE-tag containing Nb over a continuous-flow bio-catalysis system. The aldehyde group within the formylglycine side chain at the C-terminal end of the Nb is suitably located for subsequent bio-orthogonal reactions to fluorescent dyes, biotin, polyethylene glycol, or chromatography resins. We also include methods for production of high yield recombinant FGE, as well as conditions for its immobilization on Sepharose to produce the continuous-flow bio-catalysis system.

Peptide Linker Affecting the Activity Retention Rate of VHH in Immunosorbents

VHH-based immunosorbents are an emerging and promising tool for the removal of toxic substances from plasma. However, the small size of VHHs is a double-edged sword, bringing both benefits and drawbacks to the immunosorbent. The small size of the VHH allows a higher coupling density, while the closer distance to the resin might create steric hindrance for paratope access. The latter could be avoided by inserting a linker between the VHH and the gel attachment site. Here, we report an approach to improve the activity retention of the immobilized VHH by selecting suitable linkers between the VHH and the site-specific immobilization site on the resin. Seven peptide linkers differing in length and flexibility were fused to the VHH and contained the formylglycine generating enzyme (FGE) recognition sequence. These constructs were expressed in the cytoplasm of bacteria and purified, the VHH production yield and affinity for its cognate antigen was measured. Furthermore, the fGly conversion, the immobilization of the aldehyde-containing nanobodies, the immobilization on resin and the antigen binding activity of the VHH-based immunoadsorbents was monitored. The VHH with longer and rigid, proline-rich linkers exhibited good expression yield of approximately 160 mg/L of culture, a fGly conversion of up to 100%, and the highest activity retention rate of more than 68%. This study unveiled two suitable linkers for the preparation of VHH-based immunosorbents that will assist the development of their clinical application.

Design and Construction of an Effective Expression System with Aldehyde Tag for Site-Specific Enzyme Immobilization

In recent years, the development and application of site-specific immobilization technology for proteins have undergone significant advances, which avoids the unwanted and random covalent linkage between the support and active site of protein in the covalent immobilization. Formylglycine generating enzyme (FGE) can transform the cysteine from a conversed 6-amino-acid sequence CXPXR into formylglycine with an aldehyde group (also termed as “aldehyde tag”). Based on the frame of pET-28a, the His-tags were replaced with aldehyde tags. Afterward, a set of plasmids were constructed for site-specific covalent immobilization, their His-tags were knock out (DH), or were replaced at different positions: N-terminal (NQ), C-terminal (CQ), or both (DQ) respectively. Three different enzymes, thermophilic acyl aminopeptidase (EC 3.4.19.1) from Sulfolobus tokodaii (ST0779), thermophilic dehalogenase (EC 3.8.1.2) from Sulfolobus tokodaii (ST2570), and Lipase A (EC 3.1.1.3) from Bacillus subtilis (BsLA) were chosen as model enzymes to connect with these plasmid systems. The results showed that different aldehyde-tagged enzymes can be successfully covalently attached to different carriers modified with an amino group, proving the universality of the method. The new immobilized enzyme also presented better thermostability and reutilization than those of the free enzyme.

The rise of continuous flow biocatalysis – fundamentals, very recent developments and future perspectives

Very recent developments in the field of biocatalysis in continuously operated systems. Special attention on the future perspectives in this key emerging technological area ranging from process analytical technologies to digitalization.