Functional evolution of IGF2:IGF2R domain 11 binding generates novel structural interactions and a specific IGF2 antagonist

Susana Frago, Ryan Nicholls, Maddy Strickland, Jennifer Hughes, Christopher Williams, Lee Garner, Mirvat Surakhy, Rory Maclean, Dellel Aib Rezgui Rezgui, Stuart Prince, Oliver Zaccheo, Daniel Ebner, Sabina Sanegre, Sheng Yu, Francesca M Buffa, Matthew Crump, Andrew Bassim Hassan

Research output: Contribution to journalArticle (Academic Journal)

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Among the 15 extracellular domains of the mannose 6-phosphate/insulin-like growth factor-2 receptor (M6P/IGF2R), domain 11 has evolved a binding site for IGF2 to negatively regulate ligand bioavailability and mammalian growth. Despite the highly evolved structural loops of the IGF2:domain 11 binding site, affinity-enhancing AB loop mutations suggest that binding is modifiable. Here we examine the extent to which IGF2:domain 11 affinity, and its specificity over IGF1, can be enhanced, and we examine the structural basis of the mechanistic and functional consequences. Domain 11 binding loop mutants were selected by yeast surface display combined with high-resolution structure-based predictions, and validated by surface plasmon resonance. We discovered previously unidentified mutations in the ligand-interacting surface binding loops (AB, CD, FG, and HI). Five combined mutations increased rigidity of the AB loop, as confirmed by NMR. When added to three independently identified CD and FG loop mutations that reduced the koff value by twofold, these mutations resulted in an overall selective 100-fold improvement in affinity. The structural basis of the evolved affinity was improved shape complementarity established by interloop (AB-CD) and intraloop (FG-FG) side chain interactions. The high affinity of the combinatorial domain 11 Fc fusion proteins functioned as ligand-soluble antagonists or traps that depleted pathological IGF2 isoforms from serum and abrogated IGF2-dependent signaling in vivo. An evolved and reengineered high-specificity M6P/IGF2R domain 11 binding site for IGF2 may improve therapeutic targeting of the frequent IGF2 gain of function observed in human cancer.
Original languageEnglish
Pages (from-to)E2766-E2775
Number of pages11
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number20
Early online date2 May 2016
Publication statusPublished - 17 May 2016


  • growth factor receptor
  • protein evolution
  • insulin-like growth factor 2
  • binding kinetics
  • biological therapy

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