Part:BBa_K3003027

Wild Type Insulin with a Linker Peptide (SCI57)

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 is SCI-57 linker. This linker is taken from the study “Design of an active ultrastable single-chain insulin analog: synthesis, structure, and therapeutic implications” done by Hua QX et al.