Pro-islet amyloid polypeptide in micelles contains a helical prohormone segment

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Medicine

Background:

• Pro-islet amyloid polypeptide (proIAPP) is the precursor to amylin (IAPP), a hormone cosecreted with insulin involved in metabolic homeostasis.
• Amyloid plaques of IAPP and misprocessed proIAPP are hallmarks of type 2 diabetes, contributing to pancreatic β-cell destruction.
• Understanding proIAPP's interaction with cellular membranes is crucial for elucidating its role in disease pathogenesis.

Purpose of the Study:

• To determine the solution NMR structure of proIAPP bound to dodecylphosphocholine micelles.
• To investigate the membrane topology and dynamics of proIAPP.
• To explore factors influencing proIAPP's membrane affinity and its implications for prohormone processing and cosecretion.

Main Methods:

• Solution Nuclear Magnetic Resonance (NMR) spectroscopy to determine the structure of proIAPP bound to dodecylphosphocholine micelles.
• Paramagnetic relaxation enhancement (PRE) to map membrane topology.
• Circular Dichroism (CD) and diffusion-ordered spectroscopy (DOSY) to assess environmental factors affecting membrane affinity.

Main Results:

• The solution NMR structure of proIAPP bound to micelles revealed a dynamic molecule with four α-helices.
• The first two helices are within the mature IAPP sequence, and the latter two are in the C-terminal prohormone segment (Cpro).
• Paramagnetic relaxation enhancement mapped the amphipathic helices' membrane topology, and CD/DOSY identified environmental factors influencing membrane affinity.

Conclusions:

• The structural and biophysical data provide insights into proIAPP's membrane interactions and dynamics.
• Results inform understanding of prohormone processing within the regulated secretory pathway, considering varied pH and lipid environments.
• The findings suggest the potential for Cpro segment survival during cosecretion with mature IAPP, impacting disease mechanisms.