A shortened insulin with full in vitro potency.

Area of Science:

• Biochemistry
• Endocrinology
• Protein Chemistry

Background:

• Insulin's biological activity is crucial for glucose homeostasis.
• Modifications to the insulin B chain can alter its receptor binding and efficacy.
• The C-terminal region of the insulin B chain plays a role in receptor interaction.

Purpose of the Study:

• To synthesize and characterize a des[(B26-30)-pentapeptide]insulin analogue.
• To investigate the impact of C-terminal amidation at B25 on insulin activity.
• To understand the structural requirements for insulin receptor binding and biological function.

Main Methods:

• Trypsin-mediated semisynthesis of des[(B26-30)-pentapeptide]insulinamide.
• Chemical characterization of the synthesized analogue.
• In vitro biological activity assays.
• Circular dichroism (CD) spectroscopy for structural analysis.

Main Results:

• Des[(B26-30)-pentapeptide]insulinamide was successfully synthesized in 9% yield.
• The analogue with a free carboxylate group showed only 25% of normal insulin activity in vitro.
• The amidated analogue, des[(B26-30)-pentapeptide]insulinamide, exhibited full insulin activity.
• CD spectroscopy confirmed structural integrity and dynamics.

Conclusions:

• Neutralizing the negative charge at the B25 residue via amidation restores full insulin activity.
• The des[(B26-30)-pentapeptide]insulin structure possesses the necessary dynamic and structural features for receptor recognition and binding.
• Charge neutralization at B25 is critical for effective insulin signaling, particularly in a hydrophobic receptor environment.