Insulin-Insulin-like Growth Factors Hybrids as Molecular Probes of Hormone : Receptor Binding Specificity

Insulin, insulin-like growth factors 1 and 2 (IGF-1 and -2, respectively), and their receptors (IR and IGF-1R) are the key elements of a complex hormonal system that is essential for the development and functioning of humans. The C and D domains of IGFs (absent in insulin) likely play important roles in the differential binding of IGF-1 and -2 to IGF-1R and to the isoforms of IR (IR-A and IR-B) and specific activation of these receptors. Here, we attempted to probe the impact of IGF-1 and IGF-2 D domains (DI and DII, respectively) and the IGF-2 C domain (CII) on the receptor specificity of these hormones. For this, we made two types of insulin hybrid analogues: (i) with the C-terminus of the insulin A chain extended by the amino acids from the DI and DII domains and (ii) with the C-terminus of the insulin B chain extended by some amino acids derived from the CII domain. The receptor binding affinities of these analogues and their receptor autophosphorylation potentials were characterized. Our results indicate that the DI domain has a more negative impact than the DII domain does on binding to IR, and that the DI domain Pro-Leu-Lys residues are important factors for a different IR-A versus IR-B binding affinity of IGF-1. We also showed that the additions of amino acids that partially "mimic" the CII domain, to the C-terminus of the insulin B chain, change the binding and autophosphorylation specificity of insulin in favor of the "metabolic" IR-B isoform. This opens new venues for rational enhancement of insulin IR-B specificity by modifications beyond the C-terminus of its B chain

Insulin analogues with A-chain extended by the D-domain of IGF-1 and IGF-2

Insulin and insulin-like growth factors (IGF-1 and -2) together with their receptors take part in a complex system, which affects both basal metabolism of carbohydrates, lipids and proteins as well as cell growth, proliferation, differentiation and apoptosis. Defects in action of insulin or IGFs can lead to serious diseases such as diabetes or cancer. Both of these disorders represent nowadays one of the biggest health threats to the world's population. Insulin and IGFs induce different biological effects through their cognate receptors; two isoforms of the insulin receptor (IR-A and IR-B) and the receptor for IGF-1 (IGF-1R). These receptors bind insulin and IGFs with different affinities and induce different but partially overlapping signalling events leading towards metabolic (especially insulin) or mitogenic responses (IGFs and insulin). To understand the mechanism of action of insulin and IGFs it is important to specify which structural domains of these hormones are responsible for binding to the receptors and exerting specific effects. One region that is missing in insulin is the D-domain of IGF-1 and -2. For this reason, we decided to prepare insulin analogues with the A-chain extended by either the whole D-domain of IGF-1 or IGF-2, or by fragments of the IGF-1 D-domain in order to define the..

Synthesis and biochemical characterization of hybrid analogues of human insulin and IGF-2

The ever-increasing occurrence of diabetes mellitus brings about the need for development of new therapeutic agents to provide adequate treatment for patients. An important element in this research area is elucidation how insulin works, mainly in connection with insulin-like growth factors (IGF-1 and IGF-2), which show significant structural homology to each other. In addition, their respective receptors - insulin receptor (IR) and receptor for IGF-1 and IGF-2 (IGF-1R) - exhibit very high similarity. As a result, IGF-1 and IGF-2 can bind to IR and insulin can bind to IGF-1R. Of a particular importance is the high affinity binding of IGF-2 to the isoform A of IR. Unlike insulin, which predominantly mediates glucose entry into cells, IGFs induce growth or mitogenic effects. The finding which structural determinants in insulin and IGFs are responsible for the differences in the activation of their cognate receptors could provide an explanation for different functional responses upon binding of these hormones to different target cells. Understanding of this mechanism could also help in the development of functionally selective analogues of these hormones. The aim of this study was the synthesis and characterization of analogues of human insulin extended at the C terminus of the B chain with the amino..