Part:BBa_K3003025

Wild Type Insulin with a Linker Peptide (Rajpal 27)

As described in the article “Regulation of Insulin Synthesis and Secretion and Pancreatic Beta-Cell Dysfunction in Diabetes”, the wild type insulin consists of A and B chains. These chains are connected via a C-peptide (connecting peptide) when insulin is first translated. C-peptide is responsible for orienting A and B chains to enable folding. After translation, a hydrophobic N-terminal signal sequence is attached to this protein sequence. This form of insulin is called preproinsulin. The N-terminal signal sequence facilitates the translocation of preproinsulin across the rough ER membrane. During translocation to ER, the signal peptide is cleaved from preproinsulin by a signal peptidase. This cleavage yields proinsulin. Proinsulin undergoes folding and formation of disulfide bonds. After gaining a 3-D confirmation in ER, proinsulin is transported to Golgi. This is where the C-peptide between A and B chains are cleaved. The cleavage of C-peptide is not possible in bacteria. However, insulin with an uncleaved C-peptide is not proper for receptor binding. Thus, insulin chains are connected via a linker peptide in this part. The linker peptide will not be cleaved, resulting in a single chain insulin (SCI) consisting insulin A chain, linker and insulin B chain. It was shown in previous studies that SCIs can bind to the insulin receptor. The linker peptide chosen for this part Rajpal-27. This linker is taken from the study “Single-Chain Insulins as Receptor Agonists” done by Rajpal G. et al. This linker provides bioactivity and affinity for single chain insulin to recognized by the receptor, therefore it increases the affinity of SCI for binding to insulin receptor. This linker is taken from the study “Single-Chain Insulins as Receptor Agonists” done by Rajpal G. et al.