When Great is not Good Enough—VHH Antibodies Engineered for 10 Fold Affinity Increase

http://blog.allelebiotech.com/2013/10/1697/

Single Domain antibodies (VHH fragments, nanobodies, or as we call them, nAbs) have been generated by injecting llamas with ligand-bound GPCR for the purpose of obtaining crystals of active-state structures. Such structural information could be critical in understanding drug functions and screening for new drugs. The unique ability of VHH fragments to fit into protein-protein complex crevices and hold proteins together was demonstrated by two Nature publications from Brian Kobilka’s group at Stanford ([1, 2], also see Allele Newsletter of Sep 4th, 2013). The nano antibody used in those studies, Nb80, showed affinity towards only the active state of the target GPCR.

However, even with an antibody as great as Nb80, the authors were only able to co-crystal GPCR beta2-adrenoceptor (b2AR) with high affinity agonists, not its natural agonists such as adrenaline. In yet another Nature paper published just now, the Kobilka lab showed that Nb80 could be further improved by 10 times in affinity, through in vitro evolution [3]. They presented Nb80 on the surface of yeast using an existing yeast display system, then applied standard limited mutagenesis and magnetic separation technologies for screening. After about 5 rounds of selection, a new version of VHH Nb6B9 was isolated that bound to ligand-loaded GPCR with a kD of 6.4 nM. For the first time, a co-crystal of b2AR-adrenoline was made.

Rasmussen et al. Nature, 2011 Structure of a nanobody-stabilized active state of the b2 adrenoceptor
Rasmussen et al. Nature, 2011 Crystal structure of the b2 adrenergic receptor–Gs protein complex
Ring et al. Nature, 2013 Adrenaline-activated structure of b2-adrenoceptor stabilized by an engineered nanobody

Allele Annouces New Products Based on Camelid Antibodies

090209 San Diego—Allele Biotech formally announced today that it has signed an agreement to distribute products from ChromoTek GmbH, a German company with a focus on camelid antibody fragment based precipitation and detection reagents. Single-domain antigen binding fragment, also called VHH or nanobody, can be derived from heavy chain-only antibodies produced by animals in the camel family. The small size and special structures of VHH enable their efficient binding into areas not normally accessible to larger IgG antibodies. Although GFP is a commonly used tag in fusion proteins for imaging, it has not yet become a widely used tag for precipitation. With the introduction of the first VHH-based research reagent GFP-Trap, GFP-fusions will become a desirable tool for pulldown. GFP-Trap is immobilized anti-GFP nanobody, which with a simple procedure, can result in quantitative depletion or isolation of GFP-fusions.



Applications of GFP-Trap may include ChIP-CHIP, CLIP, co-IP, enzyme activity analysis (see Allele Biotech’s product group main page for sample publications). Other products such as anti-RFP and anti-GFP monoclonal antibodies that may be used after GFP-fusion precipitation are now also available from Allele Biotech. “VHH fragments have great potentials in both therapeutic and basic research,” said Allele’s CEO Dr. Jiwu Wang, “The agreement will significantly strengthen Allele Biotech's position in the antibody field”. Allele Biotech started with a grant from the NIH in 2000 to develop ways to display and select antibodies. It participated in a collaborative project on yeast display for selecting antibodies against cancer antigens in 2007 for the NCI. After acquiring Orbigen in 2008, Allele has thousands of antibodies in its product line.

Camelid Antibodies--background

When it was discovered that animals in the camel family produce antibodies with no light chains, the idea that a single-domain fragment can bind as well as a full 4-chain antibody formed a breakthrough. So far it has been a relatively less known one.

Smaller antibody fragments have been tested for therapeutic uses because classical IgG antibodies are too bulky to penetrate tissues well, and very expensive to produce. Different combinations of antigen-binding variable regions are used, e.g. scFv, Fab, diabody, all to some degree of success. In comparison, the N-terminal domain of camelid antibodies, termed VHH domain, represents a naturally evolved, only 13-15 kD in size, fully functional target binding fragment with many advantages.

The only other known species outside camelidae family that has heavy chain antibodies is particular cartilaginous fish, nurse shark. Although the arrangement of CDRs is somewhat different between the camel and shark heavy chain variable regions, they share many characteristics such as extremely high stability (maintaining functions after100 C heat and extreme pH treatment).

Accumulating reports have demonstrated the therapeutic potentials of camelid antibody-based fragments in treating cancer, neural diseases, even use in hair dandruff preventing shampoo. For basic research, the tiny antigen binders can be used as tools for quantitative pull down with unmatched efficiency, recognizing previously inaccessible enzyme cleft as antigens, and providing libraries for binding partner selection.

Allele Biotech has been working on display antibody selection from its early days through an NIH grant, and recently carried out an NIH/NCI contract for scFv yeast display in collaboration with AvantGen. By working with Chromotek on camelid antibody products, we hope to combine our superior fluorescent proteins with the best antibody candidates and display technologies to move the capture and signaling fields forward in significant ways.

The product line will be formally announced by AlleleNews shortly.