Purification and characterization of a peptide from amyloid-rich pancreases of type 2 diabetic patients.

TLDR

Amyloid deposition in pancreatic islets is a common feature of type 2 diabetes, yet the monomeric structure remains unknown because of its insolubility, and its particulate, beta‑sheet–forming properties resemble those of Alzheimer amyloid, potentially impairing islet function. The study identifies a 3,905‑Da peptide, termed diabetes‑associated peptide, as a major component of amyloid‑rich pancreatic extracts from type 2 diabetic patients and absent in normal pancreas. The peptide was isolated by collagenase digestion, sonication in 70 % formic acid, followed by gel‑filtration and reverse‑phase high‑performance liquid chromatography. The 37‑residue peptide shares 46 % identity with rat and human calcitonin gene‑related peptide and contains a 16‑residue segment homologous to the insulin A chain, indicating an evolutionary relationship.

Abstract

Deposition of amyloid in pancreatic islets is a common feature in human type 2 diabetic subjects but because of its insolubility and low tissue concentrations, the structure of its monomer has not been determined. We describe a peptide, of calculated molecular mass 3905 Da, that was a major protein component of amyloid-rich pancreatic extracts of three type 2 diabetic patients. After collagenase treatment, an extract containing 20-50% amyloid was solubilized by sonication into 70% formic acid and the peptide was purified by gel filtration followed by reverse-phase high-performance liquid chromatography. We term this peptide diabetes-associated peptide, as it was not detected in extracts of pancreas from any of six normal subjects. Diabetes-associated peptide contains 37 amino acids and is 46% identical to the sequences of rat and human calcitonin gene-related peptide, indicating that these peptides are related in evolution. Sequence identities with conserved residues of the insulin A chain were also seen in a 16-residue segment. On extraction, the islet amyloid is particulate and insoluble like the core particles of Alzheimer disease. Their monomers have similar molecular masses, each having a hydropathic region that can probably form beta-pleated sheets. The accumulation of amyloid, including diabetes-associated peptide, in islets may impair islet function in type 2 diabetes mellitus.