Insulin and insulin-like growth factors I and II are closely related protein hormones. Their distinct evolution has resulted in different yet overlapping biological functions with insulin becoming a key regulator of metabolism, whereas insulin-like growth factors (IGF)-I/II are major growth factors. Insulin and IGFs cross-bind with different affinities to closely related insulin receptor isoforms A and B (IR-A and IR-B) and insulin-like growth factor type I receptor (IGF-1R). Identification of structural determinants in IGFs and insulin that trigger their specific signaling pathways is of increasing importance in designing receptor-specific analogs with potential therapeutic applications. Here, we developed a straightforward protocol for production of recombinant IGF-II and prepared six IGF-II analogs with IGF-I-like mutations. All modified molecules exhibit significantly reduced affinity toward IR-A, particularly the analogs with a Pro-Gln insertion in the C-domain. Moreover, one of the analogs has enhanced binding affinity for IGF-1R due to a synergistic effect of the Pro-Gln insertion and S29N point mutation. Consequently, this analog has almost a 10-fold higher IGF-1R/IR-A binding specificity in comparison with native IGF-II. The established IGF-II purification protocol allowed for cost-effective isotope labeling required for a detailed NMR structural characterization of IGF-II analogs that revealed a link between the altered binding behavior of selected analogs and conformational rearrangement of their C-domains.

Department of Analytical Chemistry University of Chemistry and Technology Technická 5 166 28 Prague 6 Czech Republic

Department of Organic and Biological Chemistry School of Chemistry Cantock's Close University of Bristol Bristol BS8 1TS United Kingdom

Faculty of Science Charles University Prague Albertov 6 Prague 128 43 Czech Republic

From the Institute of Organic Chemistry and Biochemistry Academy of Sciences of the Czech Republic v v i Flemingovo nám 2 166 10 Prague 6 Czech Republic

From the Institute of Organic Chemistry and Biochemistry Academy of Sciences of the Czech Republic v v i Flemingovo nám 2 166 10 Prague 6 Czech Republic Faculty of Science Charles University Prague Albertov 6 Prague 128 43 Czech Republic

From the Institute of Organic Chemistry and Biochemistry Academy of Sciences of the Czech Republic v v i Flemingovo nám 2 166 10 Prague 6 Czech Republic Institute of Molecular Genetics Academy of Sciences of the Czech Republic v v i Vídeňská 1083 142 20 Prague 4 Czech Republic and

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