Complex Formation of Human Proelastases with Procarboxypeptidases A1 and A2

Area of Science:

• Biochemistry
• Molecular Biology
• Gastroenterology

Background:

• Pancreatic proteases are secreted as inactive zymogens.
• Complex formation among zymogens is known in some species but not fully characterized in humans.
• Previous studies identified binary complexes of procarboxypeptidase A (proCPA) with proelastases in humans and pigs.

Purpose of the Study:

• To systematically investigate complex formation among human pancreatic protease zymogens.
• To characterize binding affinities and specificities between various human proelastases and procarboxypeptidases.
• To elucidate the functional consequences of zymogen complex formation on enzyme activation and stability.

Main Methods:

• Recombinant human proelastases (proCELA2A, proCELA3A, proCELA3B) and procarboxypeptidases (proCPA1, proCPA2, proCPB1) were used.
• Binding experiments were conducted to determine dissociation constants (KD) for complex formation.
• The impact of complex formation on activation kinetics of procarboxypeptidases and proelastases was assessed.

Main Results:

• Proelastase 3B (proCELA3B) formed strong complexes with procarboxypeptidase A1 (proCPA1, KD 43 nm) and even more tightly with proCPA2 (KD 18 nm).
• Proelastase 2A (proCELA2A) showed weak binding only to proCPA1 (KD 152 nm).
• Proelastase 3A (proCELA3A) did not form stable complexes, attributed to a specific amino acid substitution (Ala241Gly).
• Complex formation delayed procarboxypeptidase activation by stabilizing its inhibitory activation peptide but did not affect proelastase activation.

Conclusions:

• Complex formation among human pancreatic protease zymogens is selective, involving specific proelastase and procarboxypeptidase pairs.
• Complex formation enhances zymogen stability by stabilizing the inhibitory activation peptide, thereby controlling the activation cascade.
• Individual variations in zymogen complex formation may occur due to polymorphic variations at key amino acid positions.