Structural contribution of the A-chain loop in relaxin

Area of Science:

• Biochemistry
• Molecular Biology
• Endocrinology

Background:

• Relaxin is a peptide hormone with diverse physiological roles.
• The A chain loop of relaxin contains critical residues and a disulfide bond influencing its conformation and activity.
• Understanding structure-activity relationships is key to developing therapeutic analogs.

Purpose of the Study:

• To investigate the impact of modifications within the A chain loop (residues A10-A15) of human relaxin II on its biological activity.
• To synthesize and characterize novel relaxin analogs with altered amino acid sequences or disulfide bond arrangements.
• To elucidate the specific structural contributions of the A chain loop to relaxin's active conformation.

Main Methods:

• Site-directed sequential disulfide bond formation was employed for analog synthesis.
• Amino acid substitutions were introduced between cysteine residues (A12-A14).
• The intrachain disulfide bond (A10-A15) was eliminated or replaced.

Main Results:

• Substitution of the native human relaxin II sequence (His-Val-Gly) at A12-A14 with insulin-like sequences (Thr-Ser-Ile) or aminooctanoic acid (Aoc) led to a significant loss of biological activity.
• Replacing the cysteine pair (A10-A15) with alanine or serine also diminished activity, with serine causing a greater reduction.
• These modifications indicate the sensitivity of relaxin's biological function to alterations in the A chain loop.

Conclusions:

• The structural integrity of the A chain loop is crucial for maintaining the active conformation and biological function of relaxin.
• The distinct amino acid sequences and disulfide bond arrangements highlight fundamental differences in the structural requirements between relaxin and insulin.
• Further research into relaxin's structure-activity relationships can guide the design of more potent and specific therapeutic agents.