The structure of ghrelin.

Area of Science:

• Biochemistry
• Structural Biology
• Computational Chemistry

Background:

• Ghrelin is a 28-residue peptide hormone crucial for appetite regulation.
• Its primary structure is known, with an active core involving residues 1-5 or 1-4 and octanoyl-Ser3.
• Experimental and computational studies have explored ghrelin's structure and function.

Purpose of the Study:

• To review and discuss experimental and computational modeling studies on ghrelin structure.
• To investigate ghrelin's conformation in different pH conditions and its interaction with lipid bilayers.
• To explore the implications of ghrelin's structure for ghrelin receptor interactions.

Main Methods:

• Review of existing literature on ghrelin structure.
• Analysis of (1)H Nuclear Magnetic Resonance (NMR) spectroscopy data.
• Molecular Dynamics (MD) simulations in aqueous and lipid bilayer environments.

Main Results:

• NMR studies indicated an unstructured or rapidly interconverting ghrelin structure at acidic pH.
• MD simulations revealed a stable ghrelin conformation at neutral pH over 25 ns in water and near a lipid bilayer.
• MD simulations showed ghrelin binding to lipid headgroups via specific residues (Arg15, Lys16, Glu17, Ser18) without octanoyl side chain insertion into the bilayer.

Conclusions:

• Ghrelin's structure is highly dependent on pH and its environment.
• The stable conformation observed near lipid bilayers, involving specific residues, is significant for receptor binding.
• Findings provide insights into ghrelin-receptor interactions and highlight limitations in current experimental and computational methods.