Purification and characterization of insulin and the C-peptide of proinsulin from Przewalski’s horse, zebra, rhino, and tapir (Perissodactyla).

This study examines the purification and characterization of insulin and the C-peptide of proinsulin from various species within the order Perissodactyla, which includes Przewalski’s horse, zebra, rhino, and tapir. Researchers found that the primary structure of insulin is highly conserved within these species, with only slight variations in the amino acid sequences. However, the structure of the C-peptide of proinsulin is less conserved, displaying more differences in amino acid sequences among the species.

Study Overview

• The research focuses on the primary structure of insulin and the C-peptide of proinsulin from different species in the Perissodactyla order, namely Przewalski’s horse, zebra, rhino, and tapir.
• It emphasizes molecular differences between these species, particularly insulin’s unique amino acid substitutions and indicative variations within proinsulin’s C-peptide.

Key Findings

• While the structure of insulin remains identical among the horse and zebra in the Hippomorpha suborder, it showed a single substitution at position 9 in the A-chain when compared to the white rhinoceros and mountain tapir from the Ceratomorpha suborder.
• A second form of Przewalski’s horse insulin, representing the gamma-ethyl ester of the Glu17 residue of the A-chain, was discovered by the study; it’s believed to be formed during pancreas extraction with acidified ethanol.
• Contrasting the highly conserved nature of insulin, the C-peptide of proinsulin showed less conservation. For instance, zebra C-peptide, comprising 31 amino acid residues, had a differing amino acid (Gln30–>Pro) compared to the horse species.
• Rhino C-peptide showed an even higher variance with three substitutions compared to the horse’s C-peptide. A possibility was posed that a specific substitution (Pro23–>Thr) makes rhino C-peptide more susceptible to proteolytic cleavage by a chymotrypsin-like enzyme than horse C-peptide.
• In the tapir pancreas extract, the C-peptide couldn’t be identified, suggesting more extensive proteolytic degradation than in the rhino.
• The research also indicated no signs of the expression of more than one proinsulin gene in the examined species of Perissodactyla, unlike in the Artiodactyla order (ox, pig).