Repurposing off-the-shelf antihelix antibodies for enabling structural biology

Antibodies are among the most impactful reagents in biological research and medicine. Both the immune system and recent advancements in antibody engineering technology are capable of generating potent and selective antibodies to virtually any antigen. In structural biology, antibodies and other types of engineered target-binding proteins, collectively termed “binders” hereafter, have extensively been used as crystallization chaperones, that is, enabling tools for producing high-quality crystals of otherwise extremely challenging molecular systems (1, 2). Binders can reduce conformational heterogeneity of a dynamic molecule and also provide surfaces for productive crystal contacts. Similarly, binders facilitate electron micrography (EM) studies by increasing the size of the molecular system over the detection threshold and by modifying the interaction between the sample and the EM grid (3). Although the potential impact of binders in structural biology investigation is well recognized, their application is still limited. The very nature of the high selectivity of binders necessitates custom development for each target. It takes substantial effort and expertise to generate, screen, and validate binders. In PNAS, Kim et al. (4) describe an innovative protein engineering strategy that enables the use of off-the-shelf antibodies as crystallization chaperones, with particular application for proteins other than the cognate antigen to which the antibody was developed. Off-the-shelf antibodies to a short peptide sequence, commonly called an epitope tag, are widely used in cell biology applications (5). They have dramatically simplified and facilitated the detection and isolation of a tagged antigen. Attaching an epitope tag, such as c-myc, V5, and FLAG, to the protein of interest is a simple task in design and in execution using standard recombinant DNA methods. The epitope-tagged protein can be readily detected and isolated using off-the-shelf antitag antibodies already optimized for specific applications. Unfortunately, such epitopes and antibodies are not particularly useful in crystallography or EM. … [↵][1]1Email: Shohei.Koide{at}nyumc.org. [1]: #xref-corresp-1-1