NMR and X-ray studies to probe whether the extracellular domains of IGF2R are Nature’s answer to a scalable ligand binding platform?

Nature’s ability to use an existing blue-print or design and evolve it to serve a new, perhaps unexpected purpose, is a continuing source of fascination and has led to the rich and diverse biology we observe around us. This process scales from the molecular level where changes to proteins might lead to new biochemistry that drives the huge diversity we see at the macroscopic scale. One such example of this process in action can be found in proteins that have a similar three-dimensional shape but are equipped with special hotspots that can adapt to bind or capture different molecules, which may themselves be proteins or simpler chemicals. This is exemplified in a receptor molecule that we study called insulin growth factor 2 receptor (IGF2R) (Crump & Hassan and co-workers 2012, Science 238, 1209-1213.). This 300 kDa protein contains fifteen structurally similar domains but with very different sets of surface loops that have evolved to bind a variety of ligands ranging from simple sugars (mono- and disaccharides) up to larger proteins such as Insulin Growth Factor-2 (see figure). Our fundamental interest in this receptor stems from its anti-tumour activity and role in several cancers. The diversity of its ligands is unprecedented and reveals the sophistication of this underlying scaffold and the potential for use in biotechnology and biological applications.

Jointly supervised with Dr Paul Race (School of Biochemistry)
Our initial aim is to engineer a super-affinity sugar binding domain (called a lectin) based on domain9 of this receptor that binds a sugar known as mannose-6-phosphate. This domain, for reasons we now understand based on its structure, cannot be purified as a single protein without its neighbouring domains. We do not wish to express all of these together as one of our aims is to maintain the small size of our synthetic receptor. We therefore aim to explore the potential of easily produced domain11 as a synthetic lectin by initially creating a chimeric scaffold that swaps in the binding loops of domain 9 then using molecular selection techniques we have in our lab (yeast surface display, NMR, X-ray and site directed mutagenesis) to explore whether this binding site can be evolved to bind mannose-6-P. If successful this may unlock the potential of these domains for binding other carbohydrates, phosphodiesters and many other ligands of choice. There has been relatively little focus so far on evolving scaffolds to target small molecules but this is changing however and there have been recent reports of using engineered anticalines for binding the well-characterized immunological hapten fluorescein with many biological applications (e.g. imaging).

Jointly supervised with Dr Paul Race (Biochemistry, UoB), collaborator Professor Bass Hassan (clinical oncologist, Oxford)