Structural properties of orexins for activation of their receptors

Area of Science:

• Neuroscience
• Molecular Biology
• Biochemistry

Background:

• Orexin A and orexin B are closely related neuropeptides.
• These peptides regulate critical physiological functions such as sleep and appetite.
• They exert their actions through the activation of orexin 1 (Ox1R) and orexin 2 (Ox2R) receptors.

Purpose of the Study:

• To elucidate the structural requirements for orexin receptor activation.
• To understand the structural basis for orexin receptor subtype selectivity.
• To investigate the role of specific amino acid residues and structural motifs in peptide-receptor interactions.

Main Methods:

• Site-directed mutagenesis was used to create modified orexin A and human orexin B-(6-28)-peptide analogs.
• Circular dichroism (CD) spectroscopy was employed to analyze the solution structures of these peptides.
• Calcium (Ca2+) mobilization assays were performed to measure the activity of the modified peptides at Ox1R and Ox2R.

Main Results:

• Basic amino acids in residues 6-14 of orexin A are crucial for activating both Ox1R and Ox2R.
• Disulfide bond restriction is not essential for maintaining the active structure of orexin A.
• The kink region in human orexin B is important for Ox2R selectivity, independent of turn structure restriction.
• No specific secondary structure is mandated for achieving receptor subtype selectivity.

Conclusions:

• Specific amino acid residues within orexin peptides play critical roles in receptor activation and selectivity.
• The structural flexibility of orexin peptides contributes to their ability to interact with different orexin receptors.
• These findings provide insights into the molecular mechanisms underlying orexin signaling and offer potential targets for therapeutic interventions.