Structural basis for the specific activation of human enteropeptidase

Area of Science:

• Biochemistry
• Enzymology
• Molecular Evolution

Background:

• Enteropeptidase is a key enzyme in digestive physiology, responsible for activating trypsinogen.
• Species-specific differences in the activation kinetics of trypsinogen by enteropeptidase have been observed.
• Understanding these differences can elucidate enzyme specificity and evolutionary relationships.

Purpose of the Study:

• To investigate the structural basis for the differential activation of human and bovine trypsinogen by human and porcine enteropeptidases.
• To determine the primary structure of the activation region of human cationic trypsinogen.
• To elucidate the evolutionary implications of species-specific enzyme-substrate interactions.

Main Methods:

• Enzyme kinetics (kcat/Km) were measured for the activation of trypsinogens by different enteropeptidases.
• Amino acid sequencing was employed to determine the N-terminal sequence of human cationic trypsinogen.
• Isolation and characterization of the activation peptide from human cationic trypsinogen.

Main Results:

• Human enteropeptidase activates human cationic trypsinogen (kcat/Km = 330 mM-1S-1) more readily than bovine trypsinogen (kcat/Km = 11 mM-1S-1).
• Porcine enteropeptidase activates bovine trypsinogen (kcat/Km = 630 mM-1S-1) more rapidly than human cationic trypsinogen (kcat/Km = 2.4 mM-1S-1).
• The activation peptide of human cationic trypsinogen is the dipeptide Asp-Lys, differing from the Val-(Asp)4-Lys peptide of bovine trypsinogen.

Conclusions:

• The unique Asp-Lys activation peptide sequence in human cationic trypsinogen is responsible for the high specificity observed with human enteropeptidase.
• Human cationic trypsinogen lacks the (Asp)4 sequence found in many other mammalian trypsinogens.
• The specific interaction between human cationic trypsinogen and human enteropeptidase suggests co-evolution of these proteins within the human lineage.