The insulin receptor. A multifunctional protein.

The insulin receptor is a multifunctional protein encoded by a modular gene. Certain discrete domains within the insulin-receptor structure subserve specific functional properties. In some instances, these discrete domains are encoded by individual exons. This organizational model of the insulin receptor predicts the existence of divergent signaling pathways facilitating specific bioeffects. Some of these signaling pathways are shared with the closely related insulinlike growth factor I receptor (convergent pathways), whereas others are different (divergent). The concept of discrete functional domains also provides several mechanisms whereby inactive insulin receptors (no kinase activity) can inhibit the function of normal receptors. The ability of kinase-inactive insulin receptors to inhibit the signaling function of normal insulin receptors may be an operative mechanism in certain insulin-resistant states.