Molecular model-building of amylin and α-calcitonin gene-related polypeptide hormones using a combination of knowledge sources

Amylin is the major component of the amyloid found in the pancreases of noninsulin-dependent diabetics (type 2 diabetes). It is a 37 amino acid polypeptide and has been shown to have 46% sequence identity with the neuropeptide α-calcitonin gene-related peptide (α-CGRP). Both amylin and α-CGRP are known to be potent inhibitors of glycogen synthesis in stripped rat soleus muscle. Secondary structure prediction and tertiary structure model-building show the two polypeptides to have an α-helix/β-strand motif similar to that observed in the insulin B-chain. The results have been supported by CD spectroscopy, although there is no sequence similarity between insulin and amylin/α-CGRP. Aggregation states have been predicted based on the dimeric and hexameric arrangements seen in porcine insulin. Rat and hamster amylin have a changed sequence motif in the β-strand which results in lack of amyloid formation and type 2 diabetes. This, we propose, is caused by disruption of hydrogen bonding which prevents the formation of the dimer.