Single domain antibodies for the knockdown of cytosolic and nuclear proteins

Abstract

Single domain antibodies (sdAbs) from camels or sharks comprise only the variable heavy chain domain. Human sdAbs comprise the variable domain of the heavy chain (VH) or light chain (VL) and can be selected from human antibodies. SdAbs are stable, nonaggregating molecules in vitro and in vivo compared to complete antibodies and scFv fragments. They are excellent novel inhibitors of cytosolic/nuclear proteins because they are correctly folded inside the cytosol in contrast to scFv fragments. SdAbs are unique because of their excellent specificity and possibility to target posttranslational modifications such as phosphorylation sites, conformers or interaction regions of proteins that cannot be targeted with genetic knockout techniques and are impossible to knockdown with RNAi. The number of inhibiting cytosolic/nuclear sdAbs is increasing and usage of synthetic single pot single domain antibody libraries will boost the generation of these fascinating molecules without the need of immunization. The most frequently selected antigenic epitopes belong to viral and oncogenic proteins, followed by toxins, proteins of the nervous system as well as plant- and drosophila proteins. It is now possible to select functional sdAbs against virtually every cytosolic/nuclear protein and desired epitope. The development of new endosomal escape protein domains and cell-penetrating peptides for efficient transfection broaden the application of inhibiting sdAbs. Last but not least, the generation of relatively new cell-specific nanoparticles such as polymersomes and polyplexes carrying cytosolic/nuclear sdAb-DNA or -protein will pave the way to apply cytosolic/nuclear sdAbs for inhibition of viral infection and cancer in the clinic.

Antibody Structure and Function: The Basis for Engineering Therapeutics

“…The elements of the engineering include having a domain to bind to the extracellular domain that permits endocytosis, a domain that improves endosomal escape efficiency, and a domain that can bind to the intracellular target [589]. Single domain antibodies have also been similarly modified for the knockdown of cytosolic and nuclear proteins [590]. The addition of endosomal escape protein domains and cell-penetrating peptides for efficient transfection broaden the application of inhibiting sdAbs.…”

Proteinaceous Regulators and Inhibitors of Protein Tyrosine Phosphatases

“…After all one could view such larger structures as composed of two distinct regions; a core scaffold fused to a bioactive peptide sequence or peptide-binding structure ( Figure 3 D–F). Many different examples have been described in the literature, ranging from decoy receptors that abrogate ligand–receptor binding [ 88 ] to antibody-derived fragments such as immunoglobin Fc domains [ 89 ] or single-chain variable fragments (scFvs) [ 90 ]. Decoy receptors result from proteolytic cleavage of genuine receptors and/or alternative splicing of receptor-encoding transcripts [ 88 ] and are of interest because of their non-immunogenicity in humans.…”

DARPins recognizing mTFP1 as novel reagents for in vitro and in vivo protein manipulations

“…Such protein binders have been used extensively, e.g. as crystallization chaperones in structural biology ( Batyuk et al, 2016 ; Manglik et al, 2017 ), as high-affinity reagents or sensors ( Borg et al, 2015 ; Braun et al, 2016 ; Kummer et al, 2013 ; Rothbauer et al, 2008 ; Trinkle-Mulcahy et al, 2008 ), as detection reagents in light and super resolution microscopy ( Pleiner et al, 2015 ; Ries et al, 2012 ) and for targeting medically relevant intracellular proteins ( Böldicke, 2017 ; Grebien et al, 2011 ; Koide et al, 2012 ), and these reports serve just as examples.…”