[21-arginine-A] insulin: a biologically active analog

Area of Science:

• Biochemistry
• Endocrinology
• Protein Chemistry

Background:

• Insulin's biological activity is crucial for glucose homeostasis.
• The A21 asparagine residue in the insulin A chain is proposed to be critical for hormone function.
• Understanding structure-activity relationships of insulin analogs can reveal insights into its mechanism of action.

Purpose of the Study:

• To synthesize and characterize a novel sheep insulin analog with arginine at the A21 position.
• To investigate the impact of substituting A21 asparagine with arginine on insulin's biological potency and activity.
• To explore the role of the A21 residue's side chain in insulin's overall function.

Main Methods:

• Synthesis of the [Arg21] A chain of sheep insulin using fragment condensation.
• Isolation of the S-sulfonated A chain derivative.
• Conversion to sulfhydryl form and interaction with S-sulfonated B chain to form [Arg21-A] sheep insulin.
• Purification using carboxymethylcellulose chromatography with a sodium chloride gradient.
• Potency assays including mouse convulsion method and radioimmunoassay.

Main Results:

• The [Arg21-A] sheep insulin analog was successfully synthesized and purified.
• The analog exhibited reduced potency, approximately 50% of natural sheep insulin (10.5–12.5 IU/mg vs. 23–25 IU/mg).
• Despite retaining proposed critical interactions, the analog's diminished activity suggests other factors influence biological function.

Conclusions:

• The substitution of A21 asparagine with arginine in sheep insulin significantly reduces biological potency.
• The A21 residue's side chain plays a role in insulin activity beyond established salt bridge and hydrogen bond interactions.
• Further investigation is needed to elucidate the specific factors involving the A21 side chain that affect insulin's biological activity.